diff --git a/.Lib9c.Benchmarks/Lib9c.Benchmarks.csproj b/.Lib9c.Benchmarks/Lib9c.Benchmarks.csproj
index a2c28e51d6..e72124db08 100644
--- a/.Lib9c.Benchmarks/Lib9c.Benchmarks.csproj
+++ b/.Lib9c.Benchmarks/Lib9c.Benchmarks.csproj
@@ -20,7 +20,7 @@
     </ItemGroup>
 
     <ItemGroup>
-      <PackageReference Include="Serilog" Version="2.10.0" />
+      <PackageReference Include="Serilog" Version="3.1.1" />
       <PackageReference Include="Serilog.Sinks.Console" Version="4.0.1" />
     </ItemGroup>
 
diff --git a/.Lib9c.Tools/Lib9c.Tools.csproj b/.Lib9c.Tools/Lib9c.Tools.csproj
index 735b45a9ec..6ab34b401b 100644
--- a/.Lib9c.Tools/Lib9c.Tools.csproj
+++ b/.Lib9c.Tools/Lib9c.Tools.csproj
@@ -20,7 +20,7 @@
 
     <ItemGroup>
       <PackageReference Include="Cocona.Lite" Version="1.5.0" />
-      <PackageReference Include="Serilog" Version="2.10.0" />
+      <PackageReference Include="Serilog" Version="3.1.1" />
       <PackageReference Include="Serilog.Sinks.Console" Version="4.0.1" />
       <PackageReference Include="Planetarium.RocksDbSharp" Version="6.2.6-planetarium" />
     </ItemGroup>
diff --git a/Lib9c/Lib9c.csproj b/Lib9c/Lib9c.csproj
index 5968cbbfc8..093643e211 100644
--- a/Lib9c/Lib9c.csproj
+++ b/Lib9c/Lib9c.csproj
@@ -22,7 +22,7 @@
   <ItemGroup>
     <PackageReference Include="DecimalMath.DecimalEx" Version="1.0.2" />
     <PackageReference Include="OptimizedPriorityQueue" Version="4.2.0" />
-    <PackageReference Include="Serilog" Version="2.10.0" />
+    <PackageReference Include="Serilog" Version="3.1.1" />
     <PackageReference Include="SonarAnalyzer.CSharp" Version="8.38.0.46746">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>