The swelling behaviors of copolymeric hydrogels containing thermosensitive poly(N-isopropyl acrylamide)[poly(NIPAAm)] in water have been investigated. Poly(N-isopropyl acrylamide-co-alkyl methacrylate)[poly(NIPAAm-co-AMA)], poly(N-isopropyl acrylamde-co-hydroxyethyl methacrylate)[poly(NIPAAm-co-HEMA)], and poly(N-isopropyl acrylamide-co-N-vinyl pyrrolidone)[poly(NIPAAm-co-NVP)] hydrogels were prepared by the solution polymerization of NIPAAm and its comonomers with AIBN at 80℃ for 40 hr. The equilibrium swelling ratios of these hydrogels were dependent upon the temperature and the comonomer such as AMA, HEMA, and NVP. The swelling ratios were decreased with an increase in the hydrophobic AMA comonomer content in the hydrogels. The lower critical solution temperatures (LCSTs) of the resulting hydrogels were decreased by the introduction of hydrophobic comonomers, whereas the LCSTs were increased by the introduction of hydrophilic comonomers in the hydrogels. These temperature dependent phenomena were also confirmed by differential scanning calorimetry.