diff --git a/CHANGELOG.md b/CHANGELOG.md
index 315a46c2..2036b999 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 - `arr.reduce`が空配列に対して初期値なしで呼び出された時、正式にエラーを出すよう
 - `str.pad_start`,`str.pad_end`を追加
 - `arr.insert`,`arr.remove`を追加
+- `arr.sort`の処理を非同期的にして高速化
 
 # 0.18.0
 - `Core:abort`でプログラムを緊急停止できるように
diff --git a/src/interpreter/primitive-props.ts b/src/interpreter/primitive-props.ts
index 4818a087..07b9a08e 100644
--- a/src/interpreter/primitive-props.ts
+++ b/src/interpreter/primitive-props.ts
@@ -246,8 +246,9 @@ const PRIMITIVE_PROPS: {
 			const mergeSort = async (arr: Value[], comp: VFn): Promise<Value[]> => {
 				if (arr.length <= 1) return arr;
 				const mid = Math.floor(arr.length / 2);
-				const left = await mergeSort(arr.slice(0, mid), comp);
-				const right = await mergeSort(arr.slice(mid), comp);
+				const left_promise = mergeSort(arr.slice(0, mid), comp);
+				const right_promise = mergeSort(arr.slice(mid), comp);
+				const [left, right] = await Promise.all([left_promise, right_promise]);
 				return merge(left, right, comp);
 			};
 			const merge = async (left: Value[], right: Value[], comp: VFn): Promise<Value[]> => {