Thermoresponsive organic-inorganic polymer hybrids were prepared from N-isopropylacrylamide (NIPA), methylenebisacrylamide (BIS), and tetramethoxysilane (TMOS) by the in situ polymerization method. The obtained PNIPA/silica polymer hybrids were examined by porosimetry, swelling degree measurement, and DSC. Samples with BIS content (the mass of BIS per the total mass of the organic component) larger than 1/100 showed excellent solvent-resistant property due to their interpenetrating polymer network (IPN) structure. The polymer hybrids swelled in water, and the swelling degree decreased continuously with raising temperature. This behavior was related to an endothermic peak of DSC analysis of the swollen hybrid, which corresponded to the dissociation of the hydrophobic interaction of PNIPA chain.