Graft polymerization of N-isopropylacrylamide (NIPA-Am) onto styrene-butadiene-styrene (SBS) block copolymer using benzoyl peroxide was studied to improve the water absorptivity and thermosensitivity of SBS. The influence of various grafting reaction factors on the conversion of NIPAAm and the grafting percentage of SBS-g-NIPAAm were also investigated in the study. The experimental results showed that the conversion of SBS-g-NIPAAm was enhanced as the monomers of NIPAAm were increased. The maximum conversion of SBS-g-NIPAAm was observed when the molar ratio of NIPAAm to butadiene was 1.25. In addition, increasing the reaction time enhanced the conversion of SBS-g-NIPAAm; the maximum grafting percentage was obtained with a 4-h reaction. The optimal concentration of the initiator was 3 X 10(-4) mol/20 mL of toluene, and the grafting reaction occurred at over 65 degreesC. The test results of the hydrophilicity of the grafted membranes showed that the hydrophilicity and thermosensitivity were significantly enhanced by grafting NIPAAm onto SBS.