The grafting of natural and synthetic polymers to form hydrogels can be done using a microwave-assisted process. It is faster, more dependable, accurate, and is able to produce product with a higher quality than the conventional approach. In this study, microwave-assisted method was applied to make polyacrylamide-grafted cassava starch (CSt-g-PAM) hydrogels using free radical potassium peroxodisulfate (KPS) as the initiator. The influence of acrylamide as the monomer and KPS as the initiator on the characteristics of the resulting hydrogel was investigated. Chemical structure of the hydrogel was studied using FTIR spectroscopy. The FTIR spectra of the CSt-g-PAM showed additional peaks indicating the presence of C=O, N–H, and C–N stretching vibrations, which confirmed the successful grafting of the polyacrylamide chains onto the backbone of the cassava starch. The absorption ability of CSt-g-PAM was evaluated using the swelling test in distilled and saline water. In distilled water, the increasing concentration of the acrylamide monomer in the reaction system improved the swelling ratio of cassava starch from 2.97 to 15.04 g/g. The improved concentration of the initiator KPS also improved the swelling ratio of the resulting polyacrylamide-grafted cassava starch from 5.17 to 10.42 g/g. The results of swelling test for CSt-g-PAM performed in the saline water provided significantly lower value than that of performed in distilled water, with the highest swelling ratio obtained of 10.57 g/g.