Bicuculline, a phthalide isoquinoline alkaloid is of current interest as an antagonist of gamma-aminobutyric acid (GABA). A simple and sensitive liquid chromatography mass spectrometry method for determination of bicuculline in rat plasma was developed over the range of 5-500ng/mL. After addition of midazolam as internal standard, protein precipitation with acetonitrile-methanol (9:1, v/v) was used as sample preparation. Chromatographic separation was achieved on a Zorbax SB-C18 (2.1mm×150mm, 5μm) column with acetonitrile -0.1% formic acid in water as mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode; selective ion monitoring (SIM) mode was used for quantification using target fragment ions m/z 368 for bicuculline and m/z 326 for the IS. Linear calibration was obtained with correlation coefficients r>0.99. The CV of the precision measurements was less than 13%. The accuracy of the method ranged from 93.6% to 100.5%. Mean recoveries of bicuculline in plasma were in the range of 80.5-91.8%. The method was successfully applied to the pharmacokinetic study after gavage administration of 15mg/kg bicuculline in rats.