diff --git a/common/serial/bytes.go b/common/serial/bytes.go
index abcf4f69..dcee4213 100644
--- a/common/serial/bytes.go
+++ b/common/serial/bytes.go
@@ -1,10 +1,8 @@
 package serial
 
-import (
-	"encoding/hex"
-	"strings"
-)
+import "encoding/hex"
 
+// ByteToHexString converts a byte into hex string.
 func ByteToHexString(value byte) string {
 	return hex.EncodeToString([]byte{value})
 }
@@ -34,10 +32,22 @@ func BytesToInt64(value []byte) int64 {
 		int64(value[7])
 }
 
+// BytesToHexString converts a byte array into hex string.
 func BytesToHexString(value []byte) string {
-	strs := make([]string, len(value))
-	for i, b := range value {
-		strs[i] = hex.EncodeToString([]byte{b})
+	m := hex.EncodedLen(len(value))
+	if m == 0 {
+		return "[]"
 	}
-	return "[" + strings.Join(strs, ",") + "]"
+	n := 1 + m + m/2
+	b := make([]byte, n)
+	hex.Encode(b[1:], value)
+	b[0] = '['
+	for i, j := n-3, m-2+1; i > 0; i -= 3 {
+		b[i+2] = ','
+		b[i+1] = b[j+1]
+		b[i] = b[j]
+		j -= 2
+	}
+	b[n-1] = ']'
+	return string(b)
 }
diff --git a/common/serial/bytes_test.go b/common/serial/bytes_test.go
new file mode 100644
index 00000000..4b37a42e
--- /dev/null
+++ b/common/serial/bytes_test.go
@@ -0,0 +1,26 @@
+package serial_test
+
+import (
+	"testing"
+
+	. "v2ray.com/core/common/serial"
+	"v2ray.com/core/testing/assert"
+)
+
+func TestBytesToHex(t *testing.T) {
+	assert := assert.On(t)
+
+	cases := []struct {
+		input  []byte
+		output string
+	}{
+		{input: []byte{}, output: "[]"},
+		{input: []byte("a"), output: "[61]"},
+		{input: []byte("abcd"), output: "[61,62,63,64]"},
+		{input: []byte(";kdfpa;dfkaepr3ira;dlkvn;vopaehra;dkhf"), output: "[3b,6b,64,66,70,61,3b,64,66,6b,61,65,70,72,33,69,72,61,3b,64,6c,6b,76,6e,3b,76,6f,70,61,65,68,72,61,3b,64,6b,68,66]"},
+	}
+
+	for _, test := range cases {
+		assert.String(test.output).Equals(BytesToHexString(test.input))
+	}
+}