Abstract: The oxidation of L-Tyrosine (L-Tyr) by hydrogen peroxide was strongly catalyzed by hemoglobin (Hb), leading to an enhancement of fluorescence. Mercury(Ⅱ) showed a strong fluorescence quenching effect on the system. Based on these facts, an enzymatic catalytic fluorescence quenching method for the determination of trace mercury(Ⅱ) in industrial wastwater was proposed. The influence factors such as acidity, concentrations of reactants, reaction time and coexisting ions were investigated. In NH3·H2O-NH4Cl buffer solution of pH 9.8, when the concentrations of L-Tyr, H2O2 and Hb were 8.00×10-5, 1.00×10-4, 5.00×10-7mol·L-1, respectively, the linear range for determination of mercury(Ⅱ) was 0.01-4.0 mg·L-1, with the detection limit (3s/k) of 3.33 μg·L-1. The method was used to determine trace mercury(Ⅱ) in industrial wastewater, giving results in consistent with those obtained by dithizone spectrophotometry. Recovery rates obtained by standard addition method were in the range of 97.3%-104%, and RSDs (n=6) were less than 3%.