diff --git a/docs/formatter.md b/docs/formatter.md
index f7d2f54..61993dc 100644
--- a/docs/formatter.md
+++ b/docs/formatter.md
@@ -42,7 +42,7 @@ Param should be number or numberic string.</p>
 <b>Signature:</b>
 
 ```go
-func Comma(value interface{}, symbol string) string
+func Comma(value interface{}, prefixSymbol string) string
 ```
 
 <b>Example:</b>
diff --git a/docs/formatter_zh-CN.md b/docs/formatter_zh-CN.md
index 4e97367..ad77a9a 100644
--- a/docs/formatter_zh-CN.md
+++ b/docs/formatter_zh-CN.md
@@ -41,7 +41,7 @@ import (
 <b>函数签名:</b>
 
 ```go
-func Comma(v interface{}, symbol string) string
+func Comma(v interface{}, prefixSymbol string) string
 ```
 
 <b>例子:</b>
diff --git a/formatter/formatter.go b/formatter/formatter.go
index e7fb426..a2ae4db 100644
--- a/formatter/formatter.go
+++ b/formatter/formatter.go
@@ -16,10 +16,10 @@ import (
 	"github.com/duke-git/lancet/convertor"
 )
 
-// Comma add comma to a number value by every 3 numbers from right. ahead by symbol char.
+// Comma add comma to a number value by every 3 numbers from right. ahead by prefix symbol char.
 // if value is invalid number string eg "aa", return empty string
 // Comma("12345", "$") => "$12,345", Comma(12345, "$") => "$12,345"
-func Comma(value interface{}, symbol string) string {
+func Comma(value interface{}, prefixSymbol string) string {
 	numString := convertor.ToString(value)
 
 	_, err := strconv.ParseFloat(numString, 64)
@@ -27,17 +27,26 @@ func Comma(value interface{}, symbol string) string {
 		return ""
 	}
 
+	isNegative := strings.HasPrefix(numString, "-")
+	if isNegative {
+		numString = numString[1:]
+	}
+
 	index := strings.Index(numString, ".")
 	if index == -1 {
 		index = len(numString)
 	}
 
 	for index > 3 {
-		index = index - 3
+		index -= 3
 		numString = numString[:index] + "," + numString[index:]
 	}
 
-	return symbol + numString
+	if isNegative {
+		numString = "-" + numString
+	}
+
+	return prefixSymbol + numString
 }
 
 // Pretty data to JSON string.
diff --git a/formatter/formatter_test.go b/formatter/formatter_test.go
index 5023da7..75fd560 100644
--- a/formatter/formatter_test.go
+++ b/formatter/formatter_test.go
@@ -26,6 +26,10 @@ func TestComma(t *testing.T) {
 	assert.Equal("12,345.6789", Comma(+12345.6789, ""))
 	assert.Equal("12,345,678.9", Comma(12345678.9, ""))
 	assert.Equal("123,456,789,000", Comma(123456789000, ""))
+
+	assert.Equal("-999", Comma(-999, ""))
+	assert.Equal("-1,000", Comma(-1000, ""))
+	assert.Equal("-1,234,567", Comma(-1234567, ""))
 }
 
 func TestPretty(t *testing.T) {