diff --git a/.changeset/gold-meals-march.md b/.changeset/gold-meals-march.md
new file mode 100644
index 000000000000..1ee6face08f1
--- /dev/null
+++ b/.changeset/gold-meals-march.md
@@ -0,0 +1,5 @@
+---
+"@astrojs/lit": minor
+---
+
+Removes deprecated `template` attribute and replaces deprecated domparser function
diff --git a/packages/integrations/lit/client-shim.js b/packages/integrations/lit/client-shim.js
index bf45dd9128d3..0cd344426da9 100644
--- a/packages/integrations/lit/client-shim.js
+++ b/packages/integrations/lit/client-shim.js
@@ -7,14 +7,8 @@ async function polyfill() {
 	});
 }
 
-const polyfillCheckEl = new DOMParser()
-	.parseFromString(
-		`<p><template shadowroot="open" shadowrootmode="open"></template></p>`,
-		'text/html',
-		{
-			includeShadowRoots: true,
-		}
-	)
+const polyfillCheckEl = Document
+	.parseHTMLUnsafe(`<p><template shadowrootmode="open"></template></p>`)
 	.querySelector('p');
 
 if (!polyfillCheckEl?.shadowRoot) {
diff --git a/packages/integrations/lit/client-shim.min.js b/packages/integrations/lit/client-shim.min.js
index 2e3d07ae7c07..d4dca4dd2061 100644
--- a/packages/integrations/lit/client-shim.min.js
+++ b/packages/integrations/lit/client-shim.min.js
@@ -8,7 +8,7 @@ var b = (t, n) => {
 function s() {
 	if (d === void 0) {
 		let t = document.createElement('div');
-		(t.innerHTML = '<div><template shadowroot="open" shadowrootmode="open"></template></div>'),
+		(t.innerHTML = '<div><template shadowrootmode="open"></template></div>'),
 			(d = !!t.firstElementChild.shadowRoot);
 	}
 	return d;
@@ -79,13 +79,6 @@ async function g() {
 	let { hydrateShadowRoots: t } = await Promise.resolve().then(() => (S(), v));
 	window.addEventListener('DOMContentLoaded', () => t(document.body), { once: true });
 }
-var x = new DOMParser()
-	.parseFromString(
-		'<p><template shadowroot="open" shadowrootmode="open"></template></p>',
-		'text/html',
-		{
-			includeShadowRoots: !0,
-		}
-	)
+var x = Document.parseHTMLUnsafe('<p><template shadowrootmode="open"></template></p>')
 	.querySelector('p');
 (!x || !x.shadowRoot) && g();