CHECKBOX_CHOICES = (

         ('Value1','Value1'),

         ('Value2','Value2'),

)

class EditProfileForm(ModelForm):

    interest = forms.MultipleChoiceField(required=False,

                                    widget=CheckboxSelectMultiple(),

                                    choices=CHECKBOX_CHOICES,)

    def save(self, *args, **kwargs):

        u = self.instance.user

        u.interest = self.cleaned_data['interest']

        u.save()

        profile = super(EditProfileForm, self).save(*args,**kwargs)

        return profile

[u'value1', u'value2']

u.interest = u','.join(self.cleaned_data['interest'])