A quantitative and qualitative method of ultra performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry(UPLC-MS/MS) was developed for the rapid and sensitive analysis of malachite green(MG) and its main metabolite leucomalachite green(LMG) in water and sediment sample.Water sample was extracted and cleaned up using mixed-mode cation exchange solid-phase extraction cartridges(MCX)，and sediment sample was supersonically extracted with acetonitrile-dichlorome mixture.Gradient UPLC separation was performed on a C18 column(BEH C18 1.7 μm,2.1 mm×50 mm) with acetonitrile(containing 0.1% formic acid) and 5 mmol/L ammonium acetate(containing 0.1% formic acid) as mobile phase.Mass spectrometric determination was carried out under an electrospray ionization interface(ESI) in positive ion mode and multiple reaction monitoring(MRM) mode.The calibration curves of two analytes were linear in the range of 0.2-100 μg/L with correlation coefficients not less than 0.995.The average recoveries of MG and LMG in blank water samples at three spiked concentration levels of 1.0,10.0,100 ng/L were in the range of 77%-90% with RSDs of 7.2%-11.4%,and its limit of detection(LOD) and limit of quantitation(LOQ)were 0.2 ng/L and 0.4 ng/L,respectively.The average recoveries of MG and LMG in sediment at three spiked levels of 0.20，2.00 and 20.0 μg/kg ranged from 82% to 91% with RSDs of 6.3%-11.6%,and its limit of detection(LOD) and limit of quantitation(LOQ)were 0.02 μg?kg-1 and 0.04 μg?kg-1,respectively.The method was suitable for the determination of MG and LMG residues in practically aquatic environmental water and sediment with high sensitivity and selectivity.