Effect of withdrawal time on sulfamethazine residues was investigated in the tissue of treated 12 pigs. A high-pressure liquid chromatographic assay procedure is described at a sensitivity of 2ng. Residual level in pork was 0.07 ppm, 0.10 ppm and 1.00ppm, respectively, of withdrawal times of 3 weeks, 1 week and 1 day after intramuscular administration. Residue in kidney was higher than that of muscle. Violance rate over 0.1ppm was 20.8% in pork and 41.7% in kidney on the market. Withdrawal time of 3 weeks is recommended for intramuscular administrated sulfamethazine in pig.