This study investigated weight changes of various light-cured glass-ionomer cements and other restorative materials during water immersion and compared findings with those of conventional glass-ionomer cement and light-cured resin composites. Three light-cured glass-ionomer cements, two polyacid-modified composite resins, one conventional glass-ionomer cement, and one light-cured composite resin were evaluated in this study. The weight changes of these specimens after water immersion were measured using an electronic analytical balance and adjusted according to water solubility measured at the same time weight change was measured. The results were analyzed by one-way ANOVA and Scheffé's F test at P < 0.05. The weight change of Photac-Fil Aplicap was the largest, and there were significant differences among the materials (P < 0.05). Weight change after 6 weeks' water immersion was noted in the following order: Fuji Ionomer Type II LC, Vitremer, Fuji Ionomer Type II, VariGlass VLC, Geristore V, and Clearfil AP-X. It is suggested that the amount of water sorption of light-cured glass-ionomer cements is greater than that of polyacid-modified composite resins.