Abstract: Fast responsive thermo and pH sensitive poly(N-isopropylacrylamide-co-acrylic acid) ［P(NIPAM-co-AAc)］ hydrogels were successfully prepared in aqueous NaCl solutions. The influence of NaCl concentration on the characteristics of the resulting hydrogels was investigated with Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy(SEM) and measuring swelling ratio. The results show that the chemical compositions and structures of different hydrogels are similar, but their micro morphologies are different. With the NaCl concentration increasing in the polymerization medium,the equilibrium swelling ratio of the hydrogels in 20 ℃ distilled water increases, the hydrogels exhibit stronger sensitivity to pH and temperature, and show much faster deswelling response rates.