The pharmacokinetics and elimination of sulfamonomethoxine (SMM) were investigated after single oral administration(200 mg/kg) in GIFT tilapia (genetically improved farmed tilapia) at (28±2)℃.The concentration of SMM in tissues of tilapia was determined by HPLC.The results showed that the Cmax were 22.66,7.13,45.50 and 22.77 μg/mL (μg/g),and the Tmax were 7.52,7.02,1.00/8.00 and 2.00/10 h(Tmax1/Tmax2) in blood,muscle,liver and kidney,respectively.The bimodal phenomenon,as shown in concentration-time curve of liver and kidney,indicated that there was non-homogeneous absorption in the gastrointestinal tract of tilapia.The T1/2Ke of SMM in blood,muscle,liver and kidney were 5.21,4.84,14.12 and 6.80 h respectively,suggesting that SMM was short-acting sulfa drug in tilapia.The elimination speed was the fastest in muscle,followed by blood,kidney and liver.According to the Announcement No.235 of People’s Republic of China,the MRL in foodstuffs of animal is 0.1 mg/kg,and the withdrawal period should not be less 5 d under this experiment condition.