Abstract:[Objective] The purpose was to develop some bacterial strains that could decolorize reactive black 5 effectively. [Methods] We isolated a bacterial strain which has strong decolorization ability, by the method of domestication with gradient concentrations, from activated sludge of Songjiang sewage treatment plant in Shanghai. [Results] According to its morphological, physiological characteristics and the analysis of 16S rRNA gene analyses for strain identification, >99.86 % of gene sequences in isolated strain RB5-M1 were similar to Aeromonas hydrophila compared to available gene sequences in the NCBI BLAST gene bank. [Conclusion] When the strain was cultivated in anaerobic cultural incubator (nitrogen 85%, carbon dioxide 6%), 35 °C, pH 8.0; it showed a decolorization rate performance of 94.1% for average value, 99.8% for maximum value.