To establish an ultra-performance liquid chromatographytandem mass spectrometry( UPLC-MS / MS) method for the quantification of icariin( ICA), and investigate pharmacokinetics of ICA in rats following multiple oral administration.ICA and an internal standard coumestrol( CMT) were extracted from rat plasma using ethyl acetate and separated on a BEH C18( 50 mm × 2. 1mm, 1. 7 μm) column using a gradient mobile phase of acetonitrile containing 0. 1%( V / V)formic acid and water containing 2 mmol / L ammonium formate at a flow rate of 0. 3m L / min. In negative electrospray ionization mode, multiple reaction monitoring of the precursor-product ion transitions of m / z 675. 6→351. 1 for ICA, 267. 0 →211. 1 for CMT was used for the quantification. Plasma was collected after rats were orally administered with ICA at multiple doses of 50 mg / kg.The linear calibration curve was achieved in a concentration range of 0. 5-50 ng / m L with a lower limit of quantification of0. 5 ng / m L. The value of intra- and inter-day precision was less than 11. 3% and accuracy fell in the ranges of 94. 3%-98. 7%. The recovery ranged from 81. 3% to85. 2% and the matrix effects from 94. 3% to 103. 2%. After oral administration of ICA to rats, t1 /2was( 1. 68 ± 0. 29) h, Cmaxwas( 29. 6 ± 5. 3) ng / m L, tmaxwas( 1. 00 ± 0. 00) h, AUC0- twas( 88. 4 ± 13. 9)( h·ng) / m L.The method is specific and accurate, suitable for preclinical pharmacokinetics of ICA.