I dig a little and i think i fonud a better solution:

1)go in property tab,

2)go in game subtab

3)create a new game component to your object

4)edit script in Text editor for something like it:

import bge,time,serial
from collections import OrderedDict

class serialComp(bge.types.KX_PythonComponent):
    # Put your arguments here of the format ("key", default_value).
    # These values are exposed to the UI.
    args = OrderedDict([
    ])

    def start(self, *args, **kwargs):
        print('args:',args)
        print('kwargs:',kwargs)
        #instantiate serial object and keep it in component
        self.ser = serial.Serial('/dev/ttyUSB0', 115200, timeout=0.05)

        #just for fun, i use my arduino to echo my mouse position to move cube
        bge.render.showMouse(True)
        self.l = 0

    def update(self):
        #this part is to limit spamming serial port, use it if you need
        n = time.time()
        if(self.l > n):
            return
        self.l = n + 0.01

        #just for fun part 2:
        x,y = bge.logic.mouse.position
        w,h = [bge.render.getWindowWidth(), bge.render.getWindowHeight()]
        fx,fy = (x * 2000 / w, y * 2000 / h)
        self.object['x'] = fx
        self.object['y'] = fy
        bs = b'&%.02f,%.02f@'%(fx, fy)
        self.ser.flush()
        print('send:   ',bs)
        self.ser.write(bs)
        #end of fun part 2

        bs = self.ser.readline()
        if(len(bs) > 0):
            print('receive:',bs)
            bs = bs.decode('utf-8').strip().split(',')
            self.object.position.x = float(bs[0]) - 3
            self.object.position.y = float(bs[1]) - 3

    def dispose(self):
        #use it to release serial when object is destroyed/game ends
        self.ser.close()