Abstract: A rapid liquid chromatography-electro-spray ionization tandem mass spectrometric method was developed for the quantification of epothilone B in human blood.Epothilone A was used as the internal standard(IS). Separation was performed using a C₁₈ column ( 150 mm×2.0 mm，4.6 μm) at 40 ℃.The mobile phase consisting of a mixture of acetonitril water ( containing 0.05% formic acid) (64 ∶36) was delivered at a flow rate of 0.2 mL /min;The analytes were analyzed by electro-spray ionization(ESI) in the multiple reaction monitoring mode.The precursor to product ion transitions of m/z 508.3→490.4 and m/z 494.3→476.1 were used to measure epothilone B and the IS，respectively.The linearity ranged from 0.1 to 20 ng/mL (r=0.999 5) and 5 to 500 ng/mL(r=0.999 4).The recovery and the intra- and inter-assay precisions met the requirements of bioanalytical method.The method is suitable for the quantification of epothilone B in human blood.