Abstract: Based on the fluorescence quenching action of malachite green (MG) on water soluble fluorescein (SF), a method for determination of residual amount of MG in grass carp using SF as fluorescence probe was proposed. It was found that in a B-R buffer solution, linear relationship between the magnitude of fluorescence quenching and mass concentration of MG was kept in the range within 80 μg·L-1, with detection limit (3S/N) 0.01 μg·L-1. Recovery of the method was tested by standard addition method, values of recovery found were in the range of 68.4%-83.3% with RSD (n=6) in the range of 3.4%-5.3%.