Solid heteropoly acid supported on silica gel (Cu3/2PMo12O40/SiO2) is easily used as a heterogonous, reusable and efficient catalyst for synthesis of 2-arylbenzimidazoles and 2-arylbenzothiazoles by reaction of o-phenylenediamine and o-aminothiophenol with different aldehydes under various conditions (in solvent, under solvent-free conditions, microwave and ultrasonic wave irradiation). The catalyst can be reused for several times but it will be less active. (C) 2008 Elsevier B.V. All rights reserved.