diff --git a/examples/function_test.go b/examples/function_test.go
index 81140e20..e9398240 100644
--- a/examples/function_test.go
+++ b/examples/function_test.go
@@ -12,22 +12,31 @@ func TestCaseCallFunction(t *testing.T) {
 			Name:    "run request with functions",
 			BaseURL: "https://postman-echo.com",
 			Verify:  false,
+			Variables: map[string]interface{}{
+				"n": 5,
+				"a": 12.3,
+				"b": 3.45,
+			},
 		},
 		TestSteps: []httpboomer.IStep{
 			httpboomer.Step("get with params").
-				WithVariables(map[string]interface{}{
-					"n": 5,
-					"a": 12.3,
-					"b": 3.45,
-				}).
 				GET("/get").
 				WithParams(map[string]interface{}{"foo1": "${gen_random_string($n)}", "foo2": "${max($a, $b)}"}).
 				WithHeaders(map[string]string{"User-Agent": "HttpBoomer"}).
 				Extract().
 				WithJmesPath("body.args.foo1", "varFoo1").
 				Validate().
+				AssertEqual("status_code", 200, "check status code").
 				AssertLengthEqual("body.args.foo1", 5, "check args foo1").
 				AssertEqual("body.args.foo2", "12.3", "check args foo2"), // notice: request params value will be converted to string
+			httpboomer.Step("post json data with functions").
+				POST("/post").
+				WithHeaders(map[string]string{"User-Agent": "HttpBoomer"}).
+				WithJSON(map[string]interface{}{"foo1": "${gen_random_string($n)}", "foo2": "${max($a, $b)}"}).
+				Validate().
+				AssertEqual("status_code", 200, "check status code").
+				AssertLengthEqual("body.json.foo1", 5, "check args foo1").
+				AssertEqual("body.json.foo2", 12.3, "check args foo2"),
 		},
 	}
 
diff --git a/runner.go b/runner.go
index 809fb0d1..4a39e7ad 100644
--- a/runner.go
+++ b/runner.go
@@ -114,7 +114,8 @@ func (r *Runner) runStepRequest(step *TStep) (stepData *StepData, err error) {
 		v = append(v, data)
 	}
 	if step.Request.JSON != nil {
-		v = append(v, req.BodyJSON(step.Request.JSON))
+		jsonData := parseData(step.Request.JSON, step.Variables)
+		v = append(v, req.BodyJSON(jsonData))
 	}
 
 	for cookieName, cookieValue := range step.Request.Cookies {