diff --git a/package/samplers/demo/README.md b/package/samplers/demo/README.md
index 72bf09b3..83fe52d4 100644
--- a/package/samplers/demo/README.md
+++ b/package/samplers/demo/README.md
@@ -5,7 +5,6 @@ description: 'Demo Sampler of OptunaHub'
 tags: ['sampler']
 optuna_versions: [3.6.1]
 license: 'MIT'
-lastmod: 2024-04-22T18:42:26+09:00
 ---
 
 This package provides a demo sampler of OptunaHub.
diff --git a/package/samplers/simple/README.md b/package/samplers/simple/README.md
index 182a2017..12fa21cf 100644
--- a/package/samplers/simple/README.md
+++ b/package/samplers/simple/README.md
@@ -5,7 +5,6 @@ description: 'An easy sampler base class to implement custom samplers.'
 tags: ['sampler', 'development']
 optuna_versions: [3.6.1]
 license: 'MIT'
-lastmod: 2024-04-17T18:42:26+09:00
 ---
 
 Simple Sampler
diff --git a/package/samplers/simulated_annealing/README.md b/package/samplers/simulated_annealing/README.md
index cd41cb15..f72d300d 100644
--- a/package/samplers/simulated_annealing/README.md
+++ b/package/samplers/simulated_annealing/README.md
@@ -5,7 +5,6 @@ description: 'Sampler based on simulated annealing algorithm.'
 tags: ['sampler', 'simulated annealing']
 optuna_versions: [3.5, 3.6]
 license: 'MIT'
-lastmod: 2024-04-07T18:42:26+09:00
 ---
 
 Simulated Annealing Sampler
diff --git a/package/visualization/plot_hypervolume_history_with_rp/README.md b/package/visualization/plot_hypervolume_history_with_rp/README.md
index 0a25e6cf..3dcc9938 100644
--- a/package/visualization/plot_hypervolume_history_with_rp/README.md
+++ b/package/visualization/plot_hypervolume_history_with_rp/README.md
@@ -5,7 +5,6 @@ description: 'Plot hypervolume history with the reference point information.'
 tags: ['visualization', 'hypervolume', 'multi-objective optimization']
 optuna_versions: ['3.6']
 license: MIT
-lastmod: 2024-04-07T18:42:26+09:00
 ---
 
 Plot Hypervolume History with Reference Point