Abstract: UHPLC-MS/MS was applied to the determination of residual amounts of malachite green and its metabolite in aquatic product. The sample was treated by homogeneous extraction with extracting agent of mixed solution of hydroxylamine hydrochloride, toluene-p-sulfonic acid and ammonium acetate, and then extracted with acetonitrile. Phase-separation was attained by freezing centrifugation at -18 ℃. ACQUITY UPLC BEH C18 column was used as stationary phase and a mixture of acetonitrile and 5 mmol·L-1 ammonium acetate (75+25) was used as mobile phase in chromatographic separation. Positive electrospray ionization was used in the detection. The malachite green D5 and leuco-malachite green D6 were used as internal standards. Linearity ranges of malachite green and leuco-malachite green were found same between 1.0-20.0 μg·L-1 with detection limits (3S/N) of 0.05, 0.06 μg·kg-1 respectively. Tests for recovery were made by standard addition method at 3 concentration levels of 1.0, 2.0, 5.0 μg·kg-1, giving values of recovery and RSD′s (n=6) in the ranges of 90.2%-106% and 2.1%-11% respectively.