diff --git a/changelog/add-pass-blocks-checkout-appearance-on-init-woopay b/changelog/add-pass-blocks-checkout-appearance-on-init-woopay
new file mode 100644
index 00000000000..ae92e257557
--- /dev/null
+++ b/changelog/add-pass-blocks-checkout-appearance-on-init-woopay
@@ -0,0 +1,4 @@
+Significance: patch
+Type: add
+
+Pass Blocks checkout appearance on init WooPay
diff --git a/client/checkout/api/index.js b/client/checkout/api/index.js
index a5fa5991fbe..a59682bd725 100644
--- a/client/checkout/api/index.js
+++ b/client/checkout/api/index.js
@@ -11,6 +11,7 @@ import {
 	getExpressCheckoutAjaxURL,
 	getExpressCheckoutConfig,
 } from 'utils/express-checkout';
+import { getAppearance } from 'checkout/upe-styles';
 
 /**
  * Handles generic connections to the server and Stripe.
@@ -459,8 +460,11 @@ export default class WCPayAPI {
 			this.isWooPayRequesting = true;
 			const wcAjaxUrl = getConfig( 'wcAjaxUrl' );
 			const nonce = getConfig( 'initWooPayNonce' );
+			const appearance = getAppearance( 'blocks_checkout' );
+
 			return this.request( buildAjaxURL( wcAjaxUrl, 'init_woopay' ), {
 				_wpnonce: nonce,
+				appearance: appearance,
 				email: userEmail,
 				user_session: woopayUserSession,
 				order_id: getConfig( 'order_id' ),
diff --git a/client/checkout/api/test/index.test.js b/client/checkout/api/test/index.test.js
index 93b135555dd..d1941846d5b 100644
--- a/client/checkout/api/test/index.test.js
+++ b/client/checkout/api/test/index.test.js
@@ -22,6 +22,33 @@ jest.mock( 'wcpay/utils/checkout', () => ( {
 	getConfig: jest.fn(),
 } ) );
 
+const mockAppearance = {
+	rules: {
+		'.Block': {},
+		'.Input': {},
+		'.Input--invalid': {},
+		'.Label': {},
+		'.Tab': {},
+		'.Tab--selected': {},
+		'.Tab:hover': {},
+		'.TabIcon--selected': {
+			color: undefined,
+		},
+		'.TabIcon:hover': {
+			color: undefined,
+		},
+		'.Text': {},
+		'.Text--redirect': {},
+	},
+	theme: 'stripe',
+	variables: {
+		colorBackground: '#ffffff',
+		colorText: undefined,
+		fontFamily: undefined,
+		fontSizeBase: undefined,
+	},
+};
+
 describe( 'WCPayAPI', () => {
 	test( 'does not initialize woopay if already requesting', async () => {
 		buildAjaxURL.mockReturnValue( 'https://example.org/' );
@@ -48,6 +75,7 @@ describe( 'WCPayAPI', () => {
 		getConfig.mockImplementation( ( key ) => {
 			const mockProperties = {
 				initWooPayNonce: 'foo',
+				appearance: mockAppearance,
 				order_id: 1,
 				key: 'testkey',
 				billing_email: 'test@example.com',
@@ -60,6 +88,7 @@ describe( 'WCPayAPI', () => {
 
 		expect( request ).toHaveBeenLastCalledWith( 'https://example.org/', {
 			_wpnonce: 'foo',
+			appearance: mockAppearance,
 			email: 'foo@bar.com',
 			user_session: 'qwerty123',
 			order_id: 1,
diff --git a/client/checkout/woopay/express-button/express-checkout-iframe.js b/client/checkout/woopay/express-button/express-checkout-iframe.js
index 2454564c88c..3e567320aa6 100644
--- a/client/checkout/woopay/express-button/express-checkout-iframe.js
+++ b/client/checkout/woopay/express-button/express-checkout-iframe.js
@@ -16,6 +16,7 @@ import {
 	appendRedirectionParams,
 } from '../utils';
 import { getTracksIdentity } from 'tracks';
+import { getAppearance } from 'wcpay/checkout/upe-styles';
 
 export const expressCheckoutIframe = async ( api, context, emailSelector ) => {
 	const woopayEmailInput = await getTargetElement( emailSelector );
@@ -106,6 +107,7 @@ export const expressCheckoutIframe = async ( api, context, emailSelector ) => {
 					order_id: getConfig( 'order_id' ),
 					key: getConfig( 'key' ),
 					billing_email: getConfig( 'billing_email' ),
+					appearance: getAppearance( 'blocks_checkout' ),
 				}
 			).then( ( response ) => {
 				if ( response?.data?.session ) {
diff --git a/client/checkout/woopay/express-button/test/woopay-express-checkout-button.test.js b/client/checkout/woopay/express-button/test/woopay-express-checkout-button.test.js
index b3ac7c41f3f..438d53c71d9 100644
--- a/client/checkout/woopay/express-button/test/woopay-express-checkout-button.test.js
+++ b/client/checkout/woopay/express-button/test/woopay-express-checkout-button.test.js
@@ -70,6 +70,32 @@ describe( 'WoopayExpressCheckoutButton', () => {
 	const mockRequest = jest.fn().mockResolvedValue( true );
 	const mockAddToCart = jest.fn().mockResolvedValue( true );
 	const api = new WCPayAPI( {}, mockRequest );
+	const mockAppearance = {
+		rules: {
+			'.Block': {},
+			'.Input': {},
+			'.Input--invalid': {},
+			'.Label': {},
+			'.Tab': {},
+			'.Tab--selected': {},
+			'.Tab:hover': {},
+			'.TabIcon--selected': {
+				color: undefined,
+			},
+			'.TabIcon:hover': {
+				color: undefined,
+			},
+			'.Text': {},
+			'.Text--redirect': {},
+		},
+		theme: 'stripe',
+		variables: {
+			colorBackground: '#ffffff',
+			colorText: undefined,
+			fontFamily: undefined,
+			fontSizeBase: undefined,
+		},
+	};
 
 	beforeEach( () => {
 		expressCheckoutIframe.mockImplementation( () => jest.fn() );
@@ -145,6 +171,8 @@ describe( 'WoopayExpressCheckoutButton', () => {
 					return 'testkey';
 				case 'order_id':
 					return 1;
+				case 'appearance':
+					return mockAppearance;
 				default:
 					return 'foo';
 			}
@@ -170,6 +198,7 @@ describe( 'WoopayExpressCheckoutButton', () => {
 				order_id: 1,
 				key: 'testkey',
 				billing_email: 'test@test.com',
+				appearance: mockAppearance,
 			} );
 			expect( expressCheckoutIframe ).not.toHaveBeenCalled();
 		} );
diff --git a/client/checkout/woopay/express-button/woopay-express-checkout-button.js b/client/checkout/woopay/express-button/woopay-express-checkout-button.js
index b7896b0549a..8011dec8eef 100644
--- a/client/checkout/woopay/express-button/woopay-express-checkout-button.js
+++ b/client/checkout/woopay/express-button/woopay-express-checkout-button.js
@@ -21,6 +21,7 @@ import {
 	deleteSkipWooPayCookie,
 } from 'wcpay/checkout/woopay/utils';
 import WooPayFirstPartyAuth from 'wcpay/checkout/woopay/express-button/woopay-first-party-auth';
+import { getAppearance } from 'wcpay/checkout/upe-styles';
 
 const BUTTON_WIDTH_THRESHOLD = 140;
 
@@ -268,6 +269,7 @@ export const WoopayExpressCheckoutButton = ( {
 					order_id: getConfig( 'order_id' ),
 					key: getConfig( 'key' ),
 					billing_email: getConfig( 'billing_email' ),
+					appearance: getAppearance( 'blocks_checkout' ),
 				} )
 					.then( async ( response ) => {
 						if ( response?.blog_id && response?.data?.session ) {
diff --git a/includes/woopay/class-woopay-session.php b/includes/woopay/class-woopay-session.php
index 02aa58a38ec..8488354ad4f 100644
--- a/includes/woopay/class-woopay-session.php
+++ b/includes/woopay/class-woopay-session.php
@@ -319,8 +319,10 @@ public static function get_frontend_init_session_request() {
 		$key           = ! empty( $_POST['key'] ) ? sanitize_text_field( wp_unslash( $_POST['key'] ) ) : null;
 		$billing_email = ! empty( $_POST['billing_email'] ) ? sanitize_text_field( wp_unslash( $_POST['billing_email'] ) ) : null;
 		// phpcs:enable
+		// phpcs:disable WordPress.Security.NonceVerification.Missing, WordPress.Security.ValidatedSanitizedInput.MissingUnslash, WordPress.Security.ValidatedSanitizedInput.InputNotSanitized, Generic.Arrays.DisallowLongArraySyntax.Found
+		$appearance = ! empty( $_POST['appearance'] ) ? self::array_map_recursive( array( __CLASS__, 'sanitize_string' ), $_POST['appearance'] ) : null;
 
-		$session = self::get_init_session_request( $order_id, $key, $billing_email );
+		$session = self::get_init_session_request( $order_id, $key, $billing_email, null, $appearance );
 
 		return WooPay_Utilities::encrypt_and_sign_data( $session );
 	}
@@ -416,9 +418,10 @@ private static function get_user_email( $user ) {
 	 * @param string|null          $key Pay-for-order key.
 	 * @param string|null          $billing_email Pay-for-order billing email.
 	 * @param WP_REST_Request|null $woopay_request The WooPay request object.
+	 * @param array                $appearance Merchant appearance.
 	 * @return array The initial session request data without email and user_session.
 	 */
-	public static function get_init_session_request( $order_id = null, $key = null, $billing_email = null, $woopay_request = null ) {
+	public static function get_init_session_request( $order_id = null, $key = null, $billing_email = null, $woopay_request = null, $appearance = null ) {
 		$user             = wp_get_current_user();
 		$is_pay_for_order = null !== $order_id;
 		$order            = wc_get_order( $order_id );
@@ -500,6 +503,7 @@ public static function get_init_session_request( $order_id = null, $key = null,
 				],
 			],
 			'tracks_user_identity' => WC_Payments::woopay_tracker()->tracks_get_identity(),
+			'appearance'           => $appearance,
 		];
 
 		$woopay_adapted_extensions = new WooPay_Adapted_Extensions();
@@ -526,6 +530,33 @@ public static function get_init_session_request( $order_id = null, $key = null,
 		return $request;
 	}
 
+	/**
+	 * Recursively map an array.
+	 *
+	 * @param callable $callback The sanitize_text_field function.
+	 * @param array    $array    The nested array.
+	 *
+	 * @return array A new appearance array.
+	 */
+	private static function array_map_recursive( $callback, $array ) {
+		$func = function ( $item ) use ( &$func, &$callback ) {
+			return is_array( $item ) ? array_map( $func, $item ) : call_user_func( $callback, $item );
+		};
+
+		return array_map( $func, $array );
+	}
+
+	/**
+	 * Sanitize a string.
+	 *
+	 * @param string $item A string.
+	 *
+	 * @return string The sanitized string.
+	 */
+	private static function sanitize_string( $item ) {
+		return sanitize_text_field( wp_unslash( $item ) );
+	}
+
 	/**
 	 * Used to initialize woopay session.
 	 *
@@ -544,8 +575,9 @@ public static function ajax_init_woopay() {
 		$order_id      = ! empty( $_POST['order_id'] ) ? absint( wp_unslash( $_POST['order_id'] ) ) : null;
 		$key           = ! empty( $_POST['key'] ) ? sanitize_text_field( wp_unslash( $_POST['key'] ) ) : null;
 		$billing_email = ! empty( $_POST['billing_email'] ) ? sanitize_text_field( wp_unslash( $_POST['billing_email'] ) ) : null;
+		$appearance    = ! empty( $_POST['appearance'] ) ? self::array_map_recursive( array( __CLASS__, 'sanitize_string' ), $_POST['appearance'] ) : null; // phpcs:disable WordPress.Security.ValidatedSanitizedInput.MissingUnslash, WordPress.Security.ValidatedSanitizedInput.InputNotSanitized, Generic.Arrays.DisallowLongArraySyntax.Found
 
-		$body                 = self::get_init_session_request( $order_id, $key, $billing_email );
+		$body                 = self::get_init_session_request( $order_id, $key, $billing_email, null, $appearance );
 		$body['user_session'] = isset( $_REQUEST['user_session'] ) ? sanitize_text_field( wp_unslash( $_REQUEST['user_session'] ) ) : null;
 
 		$args = [