Under conditions of microwave radiation (MW) and open-vessel reflux, acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) were grafted to corn starch (St) by aqueous solution polymerization in air atmosphere. Continuous MW in conjunction with potassium persulfate (KPS) were utilized to initiate the above graft reaction. A representative copolymer of St-graft-poly(AM-DADMAC) was characterized by Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy and energy disperse spectroscopy. Microwave power, radiation time, KPS concentration and AM/DADMAC molar ratio were investigated to examine their effects on grafting efficiency (GE) and cationic degree (CD). The optimal conditions under investigation were microwave power 500 W, radiation time 150 s, KPS concentration 2 mmol·L–1, AM/DADMAC molar ratio 9∶1. The GE and CD obtained were 68.6% and 0.16 mmol·g–1, respectively.