Methacrylamide (MAam) as a reactive monomer was efficiently grafted onto pregelled starch (PSt) as a natural carbohydrate polymer by a microwave initiation technique without using initiator in open vessels reactor. The latter, is fast, highly reliable, reproducible and yields high value grafted product when compared to the conventional method. Radiation time, monomer and pregelled starch concentration as well as microwave power were investigated systematically to examine their effect on maximizing the percent graft yield. The resultant microwave synthesized graft copolymer was characterized using fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) in addition to specific viscosity, swelling behavior, flocculation efficiency and Hg2+ ion removal. It is seen from the obtained results that (a) the optimum grafting conditions were found to be as follows: pregelled starch, 2 g; methacrylamide, 4 g; microwave irradiation power, 500 W, reaction time 120 S, (b) FT-IR spectral analysis confirmed amide group grafting onto pregelled starch, (c) SEM studies confirmed the surface morphology change in grafted polymer in comparison with undrafted one, (d) the specific viscosity, swelling behavior, Hg2+ ion removal and flocculation efficiency of all different levels of the copolymers used are higher than that of pregelled starch as a starting substrate, and (e) microwave initiation method proved to be a very efficient tool in comparison with other chemical initiator systems especially with respect to graft yield.