A sensitive and reproducible electro-spray ionization liquid chromatography-mass spectrometry （ESI-LC-MS） method was developed and validated to determine the concentration of nifedipine in human plasma. Following a simple liquid-liquid extraction with methylene chloride, nifedipine and nitrendipine （used as internal standard, IS） were separated on a Diamonsil ODS column （150 mm×4.6 mm, 5 μm） by isocratic elution with acetonitrile-5 mmol/L ammonium acetate （52：48, v/v） at the flow rate of 1 mL/min, and detected by mass spectrometry in the selected ion monitoring （SIM） mode. The pseudomolecular ions [M＋Na]^＋ （m/z 369.0 for nifedipine and 383.1 for nitrendipine） were selected as the target ions for quantification with fragment electric voltage of 110 V for nifedipine and 100 V for IS. Method validation demonstrated that the developed method had excellent specificity and sensitivity, and acceptable precision and accuracy. Good linearity was achieved over a wide range of （2400） gg/L （r^2〉0.998）. The plasma samples were stable after storing for more than 14 d and after two freeze-thaw cycles （-20 ℃ to 25 ℃）. The method was successfully applied to clinical pharmacokinetic studies of nifedipine.
