Abstract. Sulfadiazine monomer (SDM) was synthesized by the reaction of sulfadiazine with acryloyl chloride. The SDM was characterized by 1 H-NMR and IR spectra. A novel hydrogel with -SO2NH-group was obtained by the radical copolymerization of SDM with N-vinyl-pyrrolidone (NVP). Effects of the reaction temperature, reaction time, the monomer ratio, and the amount of the cross-linker on the pH sensitivity of the hydrogel were investigated. Results indicate that the hydrogel shows strong pH sensitivity in the pH range of 6.5 to 7.2. It also exhibits a good swelling reversibility at buffer solutions of pH 6.5 and 7.2. At last, drugs tests demonstrated the release effect of the hydrogel in pH range of 6.5 to 7.2.