Various solid acid catalysts such as HY-zeolite, silica-supported sulfuric acid, H3PW12O40, H3PMo12O40, and H3PW12O40/SiO2 have been used for the synthesis of 4-amino-pyrazolo[3,4-d]pyrimidine derivatives from the reaction of 1-substituted-5-amino-4-cyano-pyrazoles and formamid under classical heating and microwave irradiation. The microwave-solid acid combination, leads to a nice and convenient catalytic synthesis of 4-aminopyrazolo[3,4-d]pyrimidines with much reduced reaction times compared to traditional conditions. Among the above catalysts, heteropolyacid, H3PW12O40 showed the best catalytic activity in term of yields and reaction times. (c) 2006 Elsevier B.V All rights reserved.