A laboratory incubation experiment was conducted to evaluate the influence of accompanying anions on microbial activities in red soils polluted with cadmium. The results indicated application of cadmium as cadmium acetate markedly inhibited the soil microbial biomass, basal respiration, urease and acid phosphatase activity compared to cadmium applied as cadmium chloride at all cadmium levels. T-test showed that soil microbial biomass, basal respiration, urease and phosphatase activity were significantly different between red soils contaminated with cadmium acetate and chloride except for the metabolic quotients (qCO₂) in red clayey soil. Similarly, there were significant effects of cadmium with different anions on available cadmium contents in red soils after incubation. The available cadmium contents in red soils polluted by cadmium acetate were more than those by cadmium chloride. Another laboratory incubation experiment was carried out to argue the effect of associated anions on microbial activities in red soils added with potassium both acetate and chloride. Its results demonstrated that accompanying acetate anion can enhance soil microbial activities, but associated chloride anion has no remarkable effect on soil microbial activities. Thus it can be seen that difference of available cadmium contents which were resulted in by accompanying anions could be one of factors determining their relative toxicity to the soil microbial activities.