diff --git a/baselib_test.go b/baselib_test.go
new file mode 100644
index 00000000..ba773343
--- /dev/null
+++ b/baselib_test.go
@@ -0,0 +1,141 @@
+package lua
+
+import (
+	"strconv"
+	"testing"
+	"time"
+)
+
+func TestOsDateFormatUTCWithTwoParam(t *testing.T) {
+	t.Setenv("TZ", "Asia/Tokyo")
+	ls := NewState()
+
+	g := ls.GetGlobal("os")
+	fn := ls.GetField(g, "date")
+
+	int64ptr := func(i int64) *int64 {
+		return &i
+	}
+	cases := []struct {
+		Name      string
+		Local     time.Time
+		Now       time.Time
+		Format    string
+		Timestamp *int64
+	}{
+		{
+			"UTCWithTwoParam",
+			time.Now(),
+			time.Now().UTC(),
+			"!*t",
+			int64ptr(time.Now().UTC().Unix()),
+		},
+		{
+			"LocalWithTwoParam",
+			time.Now(),
+			time.Now(),
+			"*t",
+			int64ptr(time.Now().Unix()),
+		},
+		{
+			"UTCWithOnlyFormatParam",
+			time.Now(),
+			time.Now().UTC(),
+			"!*t",
+			nil,
+		},
+		{
+			"LocalWithOnlyFormatParam",
+			time.Now(),
+			time.Now(),
+			"*t",
+			nil,
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.Name, func(t *testing.T) {
+			args := make([]LValue, 0)
+			args = append(args, LString(c.Format))
+			if c.Timestamp != nil {
+				args = append(args, LNumber(*c.Timestamp))
+			}
+			err := ls.CallByParam(P{
+				Fn:      fn,
+				NRet:    1,
+				Protect: true,
+			}, args...)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			result := ls.ToTable(-1)
+
+			resultMap := make(map[string]string)
+			result.ForEach(func(key LValue, value LValue) {
+				resultMap[key.String()] = value.String()
+				assertOsDateFields(t, key, value, c.Now)
+			})
+			t.Logf("%v resultMap=%+v\nnow=%+v\nLocal=%+v\nUTC=%v", c.Name, resultMap, c.Now, c.Local, c.Now.UTC())
+		})
+	}
+}
+
+func TestOsDateFormatLocalWithTwoParam(t *testing.T) {
+	t.Setenv("TZ", "Asia/Tokyo")
+	ls := NewState()
+
+	g := ls.GetGlobal("os")
+	fn := ls.GetField(g, "date")
+
+	nowLocal := time.Now()
+	nowUTC := nowLocal.UTC()
+
+	err := ls.CallByParam(P{
+		Fn:      fn,
+		NRet:    1,
+		Protect: true,
+	}, LString("*t"), LNumber(nowLocal.Unix()))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	result := ls.ToTable(-1)
+
+	resultMap := make(map[string]string)
+	result.ForEach(func(key LValue, value LValue) {
+		t.Logf("key=%v, value=%v", key, value)
+		resultMap[key.String()] = value.String()
+		assertOsDateFields(t, key, value, nowLocal)
+	})
+	t.Logf("resultMap=%+v, nowLocal=%+v, nowUTC=%v", resultMap, nowLocal, nowUTC)
+}
+
+func assertOsDateFields(t *testing.T, key LValue, value LValue, expect time.Time) {
+	switch key.String() {
+	case "year":
+		if value.String() != strconv.Itoa(expect.Year()) {
+			t.Errorf("year=%v, expect.Year=%v", value.String(), expect.Year())
+		}
+	case "month":
+		if value.String() != strconv.Itoa(int(expect.Month())) {
+			t.Errorf("month=%v, expect.Month=%v", value.String(), expect.Month())
+		}
+	case "day":
+		if value.String() != strconv.Itoa(expect.Day()) {
+			t.Errorf("day=%v, expect.Day=%v", value.String(), expect.Day())
+		}
+	case "hour":
+		if value.String() != strconv.Itoa(expect.Hour()) {
+			t.Errorf("hour=%v, expect.Hour=%v", value.String(), expect.Hour())
+		}
+	case "min":
+		if value.String() != strconv.Itoa(expect.Minute()) {
+			t.Errorf("min=%v, expect.Minute=%v", value.String(), expect.Minute())
+		}
+	case "sec":
+		if value.String() != strconv.Itoa(expect.Second()) {
+			t.Errorf("sec=%v, expect.Second=%v", value.String(), expect.Second())
+		}
+	}
+}
diff --git a/oslib.go b/oslib.go
index 256c8811..5448cc1f 100644
--- a/oslib.go
+++ b/oslib.go
@@ -23,7 +23,7 @@ func getIntField(L *LState, tb *LTable, key string, v int) int {
 		slv := string(lv)
 		slv = strings.TrimLeft(slv, " ")
 		if strings.HasPrefix(slv, "0") && !strings.HasPrefix(slv, "0x") && !strings.HasPrefix(slv, "0X") {
-			//Standard lua interpreter only support decimal and hexadecimal
+			// Standard lua interpreter only support decimal and hexadecimal
 			slv = strings.TrimLeft(slv, "0")
 			if slv == "" {
 				return 0
@@ -106,16 +106,20 @@ func osExit(L *LState) int {
 
 func osDate(L *LState) int {
 	t := time.Now()
+	isUTC := false
 	cfmt := "%c"
 	if L.GetTop() >= 1 {
 		cfmt = L.CheckString(1)
 		if strings.HasPrefix(cfmt, "!") {
-			t = time.Now().UTC()
 			cfmt = strings.TrimLeft(cfmt, "!")
+			isUTC = true
 		}
 		if L.GetTop() >= 2 {
 			t = time.Unix(L.CheckInt64(2), 0)
 		}
+		if isUTC {
+			t = t.UTC()
+		}
 		if strings.HasPrefix(cfmt, "*t") {
 			ret := L.NewTable()
 			ret.RawSetString("year", LNumber(t.Year()))