Abstract: Bacterial degradation is a viable treatment option for azo dyes containing wastewater. However, a great drawback is the generation of potentially toxic and mutagenic end products (aromatic amines) by anaerobic bacteria. This study is part of efforts to develop textile effluent bio-treatment processes to produce reusable water by decolourization and degradation of azo dyes to non toxic metabolites. The ability of fourteen bacterial strains isolated from various environmental sources to decolourize textile wastewaters aerobically using a simulated effluent made with three textile reactive azo dyes; Reactive Yellow 42 (RY 42), Reactive Blue 13 (RB 13) and Reactive Red 58 (RR 58) were investigated. Three strains showed >95% decolourization of the synthetic effluent within 24 h. The effect of culture condition (pH, temperature and media) on the degradation of methyl red, a standard azo dye, by the isolate with the highest decolourization level; identified as Micrococcus sp., was also studied. The strain showed optimum decolourization at pH and temperature around 7 and 37°C, respectively. It preferred nutrient broth to minimal media and 0.02 g dry mass decolourized 50 mL, 56 mg L-1 solution of methyl red within 6 h under adequate oxygen supply. UV-visible spectra analyses of aniline sulphate (an aromatic amine) and those of the metabolic products of methyl red suggest that methyl red was first converted to aromatic amine(s) which was subsequently mineralized by the bacterium. The high azo dyes decolorization ability of the Micrococcus strain suggested that aerobic decolourization of azo dyes could be as effective as the anaerobic counterpart if suitable organisms are employed.