The study involved isolation of bacteria possessing high potential to degrade Reactive Black azo dye in liquid medium. Eighty four strains of bacteria were isolated through enrichment technique by using Reactive Black azo dye as the source of carbon and nitrogen in the mineral salt medium. Bacterial strains showing high decolorization rate were used to optimize the decolorization of Reactive Black azo dye in liquid culture. The optimum conditions determined for the four selected bacterial strains for decolorization of Reactive Black (250 mg L -1 ) were pH 7.0, temperature 32°C, when dye solution was supplemented with 0.5% yeast extract as a co-substrate. Out of these four strains, two strains ETL-1 (Klebsiella oxytoca) and ETL-2 (Bacillus subtillis) showed an excellent potential to decolorize 500 mg L -1 Reactive Black in 6 h in the liquid broth. Journal of Bior emediation & Biodegradation