A sensitive LC-MS-MS method has been successfully applied to pharmacokinetic study of peimine and peiminine in rat plasma after oral administration of Fritillaria thunbergii Miq. exact and Fritillaria thunbergii Miq. - Glycyrrhiza uralensis Fisch. couple extract. The results indicated that plasma profiles of peimine and peiminine confirmed to two-compartment open model with weighting function of 1/C2 for data fitting and parameter estimation and the utilization with Glycyrrhiza uralensis Fisch. could decrease C(max) and prolong MRT(0-infinity) and t1/2 of peimine remarkly with the bioavailability of peimine remained practically unchanged. Meanwhile, the concentration of peimine in rat plasma was more stable. Nevertheless, there were no significant differences among all calculated parameters of peiminine.