Abstract: An LC-MS method for quantification of corosolic acid in the plasma of rats was developed to investigated the pharmacokinetics of corosolic acid in normal and diabetic rats. Corosolic acid(170 mg/kg)was orally administered to normal rats and the diabetic rats induced by streptozotocin respectively. Blood samples were obtained from the oculic horioideae vein before and after dosing at selected intervals. The concentrations of corosolic acid were determined by LC-MS and the concentration-time data were analyzed by non-compartmental method using DAS 2. 0 software. Doublet peaks were shown in both normal and diabetic rats. The c_max and AUC_{0-24 h} were significantly increased, t_1/2 was remarkably prolonged and CL/F was observably decreased compared with those in the normal rats. The status of diabetes mellitus could alter the pharmacokinetics of corosolic acid in rats. The result obtained from the present study could provide reference for the evaluation of its relevant clinical efficacy.