Objective： To establish a high performance liquid chromatography/tandem mass spectrometry （HPLC-MS） method for determination of cyclosporin A level in the whole blood. Methods： A Hypersil C8 column （65 ℃, 4.6 mm × 150 mm, 5 μm） was used with a mobile phase of acetonitrile-acetic acid （pH 4.50） 70 ： 30 at a flow rate of 1.0 ml · min^-1. Atomospheric pressure electronic spray ionization was used to quantify cyclosporin A, with the capillary voltage being 4 000 V, the flow of drying gas being 8.0 L · min^-1 , nebulizer pressure being 30 psi, and fragment voltage being 140 V. Results： The calibration curve of cyclosporin A was linear in a range of 26.68 -1 067 μg · L^-1 ： y=0. 001 1x-0. 004 6（r=0. 999 3）. The lowest limit of detection was 4. 35 μg · L^-1. The method recoveries of low, medium and high concentrations cyclosporin A were （89.81±4.91）%, （104.5±3.73）%, and （95. 17±2.33）%, respectively; the extraction recoveries of 3 concentrations were （77.64 ± 4.38）%, （78.01 ±3.79）%, and （83.02±1.59）%, respectively. The intra-day and inter-day RSD was less than 6%, and the RSD was less than 5% in 150 days. Conclusion： The present method is fast, sensitive and selective. It is suitable for clinical monitoring of cycolsporin A.