A series of pyrazolo[3,4-b]pyridines have been synthesized through the reaction of pyrazol-5-amine, arylglyoxals and malononitrile in acetic acid at 100 _oC under microwave irradiation. This method has the advantages of short reaction times (20-30min), excellent selectivity, simple operation as well as environmental friendly. The structures of products were characterized by IR, ₁HNMR, ₁₃CNMR and HRMS. Furthermore, the product 6-amino-4-(4-chlorobenzoyl)-1,3-dimethyl-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile 4a was confirmed by X-ray diffraction analysis.