Abstract: Background and Objective: Azo dyes are the most widely used synthetic colorants in industry and they are regarded as pollutants. Bioremediation through microorganisms has been identified as an effective method. The objective of this study is to examine the potential of four bacterial strains for decolorization and degradation of azo dyes produced in the final effluent of textile dying industries. Materials and Methods: Bacterial isolates of Bacillus subtilis, Bacillus cereus, Bacillus licheniformis and Pseudomonas sp., isolated from dye contaminated sludge environment were investigated for degradation of various azo dyes. Nutritional and environmental parameters affecting dye decolorization were optimized. The degradation and detoxification was confirmed by UV-vis characterization, FTIR analysis and toxicity studies. Results: Glucose was the most effective carbon source for maximum decolorization efficiency of Pseudomonas sp., for black B and congo red accounting 49.46 and 75.31%, respectively and of Bacillus subtilis for black B reached 48.68%. However, the highest congo red decolorization percentages by Bacillus cereus and Bacillus licheniformis reached 72 and 80.32%, respectively were recorded in the presence of starch. Organic nitrogen sources peptone and yeast extract were the best inducers for decolorization of black B and congo red dyes, respectively by the four strains. The decolorization of reactive dyes by bacterial strains was efficient at pH 7, temperature of 37°C, with 200 mg L–1 dye concentration and 20% (v/v) inoculum size under static condition at 72 h. The UV-vis spectra of the decolorized dyes showed disappearance of peaks, which indicated that the decolorization is due to biodegradation, rather than inactive surface adsorption. Conclusion: The toxicity test concluded that the degradation products were less toxic compared to wild dyes. The phytotoxicity study showed good germination rate as well as significant growth of Vicia faba seeds observed in degraded metabolites as compared to control. This study recommended the application of the these bacterial strains in the decolorization of the azo dyes in the industrial effluents under all nutritional and environmental conditions in Egypt.