In the present study mixed cultures that could grew in the molasses media were isolated from textile dye effluent and its decolorization activity was studied in a batch system under anaerobic conditions, in order to determine the optimal conditions required for the highest decolorization activity. The optimum pH value for decolorization was determined as 8 for all the dyes tested. In the experiment with pH 8 dye decolorizations by mixed cultures were investigated at about 96.2-1031.3 mg l(-1) initial dye concentrations. The highest dye removal rates of mixed cultures were 94.9% for Reactive Red RB, 91.0% for Reactive Black B and 63.6% for Remazol Blue at 953.2, 864.9 and 1031.3 mg l(-1) initial dye concentrations respectively within 24h incubation period. When the Reactive Red RB was used, approximately 82-98% total color removal was obtained at between 96.2 and 953.2 mg l(-1) initial dye concentrations after 12 h of incubation at 35 C. These results show that our enriched mixed cultures have the potential to serve as an excellent biomass for the use in reactive dye removal from wastewaters under anaerobic conditions. (c) 2005 Elsevier Inc. All rights reserved.