Aims: In this study, the toxicity of three metal plating wastewaters were assessed using sequencing batch reactor (SBR) bacteria. Materials and Methods: For determining the growth inhibition in each metal plating wastewater concentration, the cultured SBR bacteria on nutrient broth media were used and after exposure they cultured on nutrient agar media. Each test was performed in three replicates. Mean of three replicate were analyzed, and no observed effect concentration (NOEC), 50% effective concentration (EC50) was calculated using the probit analysis in SPSS version 16.0 software (SPSS Inc., 233 South Wacker Driv). Results: According to the probit analysis, there is no effect on tested bacteria at the concentrations of 1 mL/L, >50 mL/L and >100 mL/L of metal plating wastewaters in sample 1, 2 and 3, respectively. While almost all bacteria will be dead in the concentration of 1000 mL/L of each metal plating wastewater. Maximum and minimum EC50 were recorded for the metal plating wastewater number 3 (with value of 960 mL/L) and number 1 (with value of 6.5 mL/L). On the other hand, the calculation of NOEC using probit analysis showed that sample 1 is toxic even in minimum concentrations because its NOEC was 1.1 mL/L. Conclusion: Results of this study showed that some metal plating wastewaters in the very low concentrations could induce an adverse effect on the bacterial community structures of WWTPs biological units. Hence, it could be recommended that effluent standards and in-situ treatment rules should be applied according to the kind of process in such industries.