Abstract: OBJECTIVE To establish an LC-MS/MS method to determine azilsartan and its salt in rat plasma and investigate their pharmacokinetics. METHODS After protein precipitation with acetonitrile, the analytes and internal standard were separated on Eclipse Plus C₁₈ column(50 mm×3.0 mm, 1.8 μm) with acetonitrile-water (60:40) as mobile phase eluted at a flow rate of 0.35 mL·min^-1. Detection was carried out by electrospray positive ionization mass spectrometry in the multiple reaction monitoring(MRM) mode. The MRM transitions of m/z 457.3/233.1 and m/z 436.2/291.4 were used to quantify azilsartan and valsartan, respectively. SD rats were given azilsartan of 1.0 mg·kg^-1 while the salt of 1.2 mg·kg^-1. RESULTS The calibration curve of azilsartan was linear over the concentration range of 5-30 000 ng·mL^-1. The RSDs of accuracy were <15%. The main pharmacokinetics parameters of the salt in rats were estimated as follows:AUC_{(0-24 h)}was (12.9±3.2)μg·mL^-1·h^-1, AUC_(0-∞) was (14.2±4.1)μg·mL^-1·h^-1, C_max was (3.8±0.3)μg·mL^-1, T_1/2 was (13.4±0.5)h. The main pharmacokinetics parameters of azilsartan were estimated as follows:AUC_{(0-24 h)} was (8.1±2.6)μg·mL^-1·h^-1, AUC_(0-∞) was (9.7±3.1)μg·mL^-1·h^-1, C_max was (2.3±0.5)μg·mL^-1, T_1/2 was (10.5±0.5)h. CONCLUSION The established method can be applied on the determination of azilsartan and its salt in plasma of rats and is suitable for the pharmacokinetics study.