New derivatives of polyfunctional pyrazolo[3,4-b]pyridines were synthesised via a regioselective one-pot three-component reaction of 3- (cyanoacetyl)indole, 5-amino-3-methylpyrazole and arylaldehydes in excellent yields using Fe3+-montmorillonite as a reusable catalyst under conventional conditions and ultrasonic irradiation. In particular, valuable features of this method include high reaction rate