Can I change the font size in only one widget and keep it the same in the root window?
if yes then how please?

Most widgets have a font option.

What is your code now?

this can be done in any widget the same way but heres an example using label:

from Tkinter import *

tk=Tk()

label = Label(tk, text='new font', font='Impact 72 bold')
label.pack()

tk.mainloop()

you can use any font that is on your system

Oh thanx =) that solved it!