Abstract: At water temperature of 18℃ or 28℃,grass carp was administered orally or by intraperitoneal injection with sulphamethoxazole (SMZ) in single dose of 100mg/kg. The concentration of SMZ in the plasma and muscles of the fish were determined by high performance liquid chromatography and the concentration-time data were treated with MPKP practical pharmacokinetic software. The results showed that the elimination half-time (T 1/2α ),the elimination half-time (T 1/2β ) and the peak time of SMZ at oral administration at lower temperature were remarkably longer than those at higher temperature (P0.01). The peak concentration at lower temperature was significantly lower than that at higher temperature (P0.01). Absorption and elimination of SMZ in the plasma and muscle were quicker when administered by intraperitoneal injection than those when administered orally. and its elimination was quicker by intraperitoneal injection than at oral administration. At the temperature of 18℃,the profile of SMZ in the plasma could be described by a two-compartment open model with lag-time when administered orally. It could be described by a two-compartment model without lag-time when administered by intraperitoneal injection. At the temperature of 28℃,the profile could be described by a two-compartment open model with an illegible lag-time. Based on the pharmacokinetics of SMZ,the minimum effective blood drug concentration and the general principle in application of antibiotics,SMZ administration for grass carp is recommended to be in a 3 days treatment administered orally or by intraperitoneal injection twice a day,at 18℃ or 3-4 times a day at 28℃ at 100mg/kg.