Macroporous poly(N-isopropylamide-co-acrylamide) [P(NIPAAm-co-AAm)] hydrogels were successfully prepared by a two-step polymerization method. The initial polymerization was carried out at 18 degrees C with different duration, followed by freezing polymerization at -18 degrees C for 24 h. The results showed that the immediate performance of freezing polymerization played a dominant role in the final properties of the P(NIPAAm-co-AAm) hydrogels. The thermoresponsive rate and mechanical strength of the hydrogels were drastically changed by freezing the reaction mixture after 3 min of the first polymerization (PNA-3). Scanning electron microscopy (SEM) studies revealed that the hydrogel frozen after 3 min exhibited the most highly interconnected porous structures and the largest pore size. These open pore structures were very useful to accelerate the responsive rate of the hydrogels. In vitro BSA (bovine serum albumin) release from the hydrogel PNA-3 exhibited relatively small initial burst release followed by a steady release. Such results demonstrated that the P(NIPAAm-co-AAm) hydrogels frozen before gelation have the potential to be applicated for delivering proteins.