class MyModelAdmin(admin.ModelAdmin):

    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        if db_field.name == 'car':
            kwargs['queryset'] = Car.objects.filter(owner=request.user)
return super(MyModelAdmin, self).formfield_for_foreignkey(db_field, request,
    **kwargs)
Limiting Admin Choices Using limit_choices_to