Biodegradation of acid blue 113 has been studied using two strains-Staphylococcus aureus and Escherichia coli. The effect of pH, time, initial dye concentration, the inoculum size, the co-substrate, static and shaking on decolourisation was studied. The optimum condition for decolourisation was found to be at pH 7 for an initial dye concentration of 200 mg/L at 37 ̊C under static condition. The removal of dye by S.aureus and E.coli at optimum condition was 90% and 88% within 30 h and 42 h respectively. Addition of fructose and starch as carbon source increased the removal of colour by S.aureus and E.coli respectively. Similarly addition of ammonium formate and glycine as nitrogen source under static condition increased the colour removal by S.aureus and E. coli. The enzyme activity of azoreductase for S. aureus and E. coli was found to be 7.33 U/ml and 7.24 U/ml respectively. The COD reduction, FTIR and TLC analysis of the sample before and after decolourisation confirmed the biodegradation of dye and the formation of new metabolite. Phytotoxicity studies indicated that the microbial treated effluent is safe for disposal into the environment. .