import string, win32ui, win32con
from tkinter import *

def decaption(event):
    w = event.widget
frame = win32ui.CreateWindowFromHandle(string.atoi(w.wm_frame(), 0))
frame.ModifyStyle(win32con.WS_CAPTION, 0, win32con.SWP_FRAMECHANGED)
w.bind('<Map>', None)
root = Tk()
root.bind('<Map>', decaption)
root.mainloop()
Using TCL extensions to set native window style in Tkinter