The acute and chronic toxicity of mercury, copper, cadmium andchromium to the survival, growth, reproduction and the intrinsic rate of increase(r_m) of M. mongolica were studied. The 48 hr LC₅₀ of Hg²⁺ Cu²⁺, Cd²⁺ andCr(6) was 0.0034, 0.0888, 3.89 and 4.24 mg/l respectively. The toxicity ofcombined different metals to the organism was also studied. The result reveals thatthe toxicity of mixtures of two metals was much stronger than the single one (ex-cept Hg/Cu). While the toxicity of three or four metals combination was lower thanthat of two metals.