diff --git a/operation/wiki/wiki.go b/operation/wiki/wiki.go
index 1e4373b..b019724 100644
--- a/operation/wiki/wiki.go
+++ b/operation/wiki/wiki.go
@@ -2,6 +2,7 @@ package wiki
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"net/url"
 
@@ -40,7 +41,7 @@ var (
 		mcp.WithString("repo", mcp.Required(), mcp.Description("repository name")),
 		mcp.WithString("pageName", mcp.Description("wiki page name (required for 'update', 'delete')")),
 		mcp.WithString("title", mcp.Description("wiki page title (required for 'create', optional for 'update')")),
-		mcp.WithString("content_base64", mcp.Description("page content, base64 encoded (required for 'create', 'update')")),
+		mcp.WithString("content", mcp.Description("page content (required for 'create', 'update')")),
 		mcp.WithString("message", mcp.Description("commit message")),
 	)
 )
@@ -176,7 +177,7 @@ func createWikiPageFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTo
 	if err != nil {
 		return to.ErrorResult(err)
 	}
-	contentBase64, err := params.GetString(args, "content_base64")
+	content, err := params.GetString(args, "content")
 	if err != nil {
 		return to.ErrorResult(err)
 	}
@@ -188,7 +189,7 @@ func createWikiPageFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTo
 
 	requestBody := map[string]string{
 		"title":          title,
-		"content_base64": contentBase64,
+		"content_base64": base64.StdEncoding.EncodeToString([]byte(content)),
 		"message":        message,
 	}
 
@@ -216,13 +217,13 @@ func updateWikiPageFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallTo
 	if err != nil {
 		return to.ErrorResult(err)
 	}
-	contentBase64, err := params.GetString(args, "content_base64")
+	content, err := params.GetString(args, "content")
 	if err != nil {
 		return to.ErrorResult(err)
 	}
 
 	requestBody := map[string]string{
-		"content_base64": contentBase64,
+		"content_base64": base64.StdEncoding.EncodeToString([]byte(content)),
 	}
 
 	// If title is given, use it. Otherwise, keep current page name
diff --git a/operation/wiki/wiki_test.go b/operation/wiki/wiki_test.go
new file mode 100644
index 0000000..e72137d
--- /dev/null
+++ b/operation/wiki/wiki_test.go
@@ -0,0 +1,75 @@
+package wiki
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	mcpContext "gitea.com/gitea/gitea-mcp/pkg/context"
+	"gitea.com/gitea/gitea-mcp/pkg/flag"
+
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+func TestWikiWriteBase64Encoding(t *testing.T) {
+	tests := []struct {
+		name    string
+		method  string
+		content string
+	}{
+		{"create ascii", "create", "Hello, World!"},
+		{"create unicode", "create", "日本語テスト 🎉"},
+		{"create multiline", "create", "line1\nline2\nline3"},
+		{"update ascii", "update", "Updated content"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var gotBody map[string]string
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				body, _ := io.ReadAll(r.Body)
+				json.Unmarshal(body, &gotBody)
+				w.Header().Set("Content-Type", "application/json")
+				w.WriteHeader(http.StatusOK)
+				w.Write([]byte(`{"title":"test"}`))
+			}))
+			defer srv.Close()
+
+			origHost := flag.Host
+			flag.Host = srv.URL
+			defer func() { flag.Host = origHost }()
+
+			ctx := context.WithValue(context.Background(), mcpContext.TokenContextKey, "test-token")
+
+			args := map[string]any{
+				"method":   tt.method,
+				"owner":    "org",
+				"repo":     "repo",
+				"content":  tt.content,
+				"pageName": "TestPage",
+				"title":    "TestPage",
+			}
+
+			req := mcp.CallToolRequest{}
+			req.Params.Arguments = args
+
+			result, err := wikiWriteFn(ctx, req)
+			if err != nil {
+				t.Fatalf("wikiWriteFn() error: %v", err)
+			}
+			if result.IsError {
+				t.Fatalf("wikiWriteFn() returned error result")
+			}
+
+			got := gotBody["content_base64"]
+			want := base64.StdEncoding.EncodeToString([]byte(tt.content))
+			if got != want {
+				t.Errorf("content_base64 = %q, want %q", got, want)
+			}
+		})
+	}
+}