Effects of different waterborne mercury(Hg²⁺)(0,10,50,100,200,300 μg/L)on accumulation of mercury in the gills of juvenile Eriocheir sinensis were studied by singe gradient factor experiments.Gills of E.sinensis accumulated mercury rapidly from water environment after 40 days' exposed period.The contents of mercury in gills were 4.56,25.53 and 46.51 μg/g dry weight in 10,50 and 100 μg/L Hg²⁺ waterborne groups,whose values were significantly(P<0.05)higher than control groups.The contents of mercury were 183.75 and 283.36 μg/g dry weight in 200 and 300 μg/L Hg²⁺ groups and the accumulation rate attained to 910.35 and 939.60.Light microscopic examination showed that the histoarchitecture of gills were changed greatly in low Hg²⁺ level groups,the changes included the epithelial cells distended,the gill lamellae enlarged,the tips of gill filament swelled seriously.In the 300 μg/L groups,the normal structures of the whole gill lamellae were destroyed completely.The correlation of the accumulation of mercury in gills of E.sinensis to the concentrations of Hg²⁺ in water was analyzed by biostatistics method,and showed that there was dramatic correlation between them.Exposure to high concentrations groups Hg²⁺(mercury chloride)was found to result in several alterations in the histoarchitecture of the gills of E.sinensis,and such alterations could affect vital physiological functions,such as respiration,osmotic and ionic regulations of gills,which in turn could ultimately affect the survival and growth of E.sinensis.