An original and sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the determination of pseudoprotodioscin(PPD)in rat plasma was developed and validated.Digitoxin was applied as internal standard.Plasma samples were processed by acetonitrile-mediated plasma protein precipitation and chromatographed using a step gradient program on a C18 column (2.1 mm×50 mm i.d., 1.7 μm).The mobile phase was comprised of acetonitrile and 0.1 mmol/L aqueous lithium acetate mixed with 0.03% formic acid at the flow rate of 0.2 ml/min.