Objective:To establish a liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for determination of the losartan concentrations in rat plasma,urine and bile．Methods: The method was based on a protein precipitation procedure for rat plasma and liquid-liquid extraction for rat urine and bile,then the diluted extract was analyzed by LC/MS/MS using turbo ion spray (TIS) positive ion mode.Chromatography was performed on an Agela Venusil MP-C18 column (5 μm particle,2.1 mm×50 mm) by gradient elution.Mobile phase A was 0.1% formic acid in water and mobile phase B was 0.1% formic acid in acetonitrile.The mobile phase B increased from 20% to 95% within 1.5 min,with the flow rate being 0.35 ml/min and the feeding rate being 10 μl.Electrospray ionization (ESI) ion source was used.Results: The linear range of losartan was 1-1 000 μg/L in the plasma,urine and bile of rats (r>0.99).The mean relative recovery rate was higher than 80.0%;RSD values of intra-day and inter-day were both less than 15%.Conclusion: The present method is easy to perform,accurate,and specific; it can be used for determination of losartan concentration in rat plasma,urine and bile．