A rapid and sensitive liquid chromatography-tandem mass spectrometry method(LC-MS/MS)was developed and validated for the quantification of fexofenadine in human plasma,to conduct comparative bioavailability studies.Human plasma was extracted with a mixture of dichloromethane-diethyl ether(volume ratio 2∶3)in a basic environment and the extract was separated on a C18 column with a mobile phase consisting of acetonitrile-methanol-10 mmol/L ammonium acetate(volume ratio 45∶45∶10).The analytes were detected via electrospray ionization(ESI)tandem mass spectrometry in the multiple-reaction-monitoring(MRM)mode.The linearity was within a range of 1-1000 ng/mL.The intra-and inter-day precision were<4.1% and<4.8%,respectively,and the accuracy was in the range of 95.0%-105%.The method was applied to the quantification of fexofenadine human plasma from 20 healthy male Chinese volunteers,according to a single dose,randomized,two-way crossover design with a two-week washout period.The mean values of major pharmacokinetic parameters of ρmax,AUC0-48,AUC0-∞,tmax,and t1/2 were determined from the plasma concentration.The analysis of variance(ANOVA)did not show any significant difference between the two products of fexofenadine and 90% confidence intervals fell within the acceptable range for bioequivalence. A rapid and sensitive liquid chromatography-tandem mass spectrometry method (LC-MS / MS) was developed and validated for the quantification of fexofenadine in human plasma, to conduct comparative aerial bioavailability studies. Human plasma was extracted with a mixture of dichloromethane- diethyl ether volume ratio 2: 3) in a basic environment and the extract was separated on a C18 column with a mobile phase consisting of acetonitrile-methanol-10 mmol / L ammonium acetate (volume ratio 45:45:10). The analytes were detected via electrospray ionization (ESI) tandem mass spectrometry in the multiple-reaction-monitoring (MRM) mode. The linearity was within a range of 1-1000 ng / mL.The intra- and inter- day precision were <4.1% and <4.8% , respectively, and the accuracy was in the range of 95.0% -105%. The method was applied to the quantification of fexofenadine human plasma from 20 healthy male Chinese volunteers, according to a single dose, randomized, two-way crossover design with a two-week washout period.The mean val ues of major pharmacokinetic parameters of ρmax, AUC0-48, AUC0-∞, tmax, and t1 / 2 were determined from the plasma concentration. The analysis of variance (ANOVA) did not show any significant difference between the two products of fexofenadine and 90 % confidence intervals fell within the acceptable range for bioequivalence.