Made a simple gui string encrypter, just to obfuscate plaintext
import Tkinter
import base64

class crypt_mod(Tkinter.Tk):


Do you know about PEP8? It's a style guide for Python that lots of Python developers follow. One of the things it says is that class names should use the CapWords convention, eg. CryptMod. Note that Tkinter doesn't necessary follow those rules, as it's a really old module.

    def __init__(self, parent):
        Tkinter.Tk.__init__(self, parent)
        self.parent = parent
        self.initialize()


self.parent seems to be unused.

    def initialize(self):
        self.grid()
            ....


Not much to say here: the usual GUI building code.

    def encrypt(self):
        self.etxt.set(base64.b64encode(str(self.ptxt.get())))
        self.history.config(state='normal')
        self.history.insert(Tkinter.END, 'encrypt:\n' + base64.b64encode(str(self.ptxt.get())) + '\n')
        self.history.config(state='disabled')
        self.history.see(Tkinter.END)
        #print "encrypt click!"


Avoid creating twice your encrypted text: your code would be clearer if you had a encrypted variable. It's not terribly important here, but could be in future projects where you will have more lines of code. Consider using format() (recommended in Python 3) instead of building your strings by concatenation: "decrypt:\n {} \n".format(encrypted). (Those comments also apply to decrypt.)