A laboratory incubation experiment was conducted to elucidate the effect of acetate on lead bioavailability and toxicity to microbial biomass in a red soil. Treatment included the application of lead at six different levels i.e., 0(background), 100, 200, 300, 450 and 600μg/g soil with three levels of the acetate(0, 900 and 2700 μg/g soil). Results indicated that the application of acetate along or at the lower lead levels of 100 and 200μg/g soil stimulated the soil microbial biomass. The addition of acetate at the higher lead levels of 300, 450 and 600 μg/g soil caused significantly greater reductions in the biomass carbon(Cmic) and the biomass nitrogen(Nmic), compared with the control or the same lead levels applied individually. A greater increase in the biomass C:N ratio occurred by acetate addition at the same lead levels. The concentration of 0.01mol/L CaCl2-extractable lead was considerably higher in the lead plus acetate treatments than at the same lead levels with no acetate.Based on these results, it was concluded that the application of acetate might have suppressed the lead adsorption in the soil which in turn resulted in its more bioavailability and hence more toxicity to the soil microbial biomass.