OBJECTIVE:To establish the method to determine the concentration of human plasma felodipine by HPLC-MS.METHODS:The HPLC separating system was adopted and the mobile phase was a mixture of methanol-water-acetic acid with a flow rate at1ml/min and split ratio at2∶1,the fixed phase was Hypersil C 18 column;The mass spectrometric de-tection system and AP-ESI positive ion model were adopted with the atmosperic pressure at0.054Pa(400psi),the protecting gas at N 2 10L/min,capillary voltage at4000V,the ion source temperature at100℃and the fragment voltage at220V,the ions collected by SIM were felodipine m/z411(M+Na),Nimodipine m/z441(M+Na).RESULTS:The linear concentration range for felodipine was0.2～50ng/ml with a minimum detection limit at0.15ng/ml,the recovery was above90.93%with both the intra-day RSD and the inter-day RSD at less than9.8%(RSD