The aim of this work is to isolate and characterize bacterial isolates form dye house effluent, and to check their ability of decolorizing sulfonated azo dyes, and also to study influence of various environmental parameters on same process. Among seven Gram positive bacterial isolates obtained form dye house effluent, M1 (Bacillus cereus) and M6 were proved to be more potent for decolorizing sulfonated azo dyes under aerobic conditions. Maltose as carbon source and peptone as nitrogen source enhanced decolorization efficiency of M1 (B. cereus). HPTLC studies proved that more than 97% of the dye (Reactive Red195) was degraded by bacteria after 72 h of incubation. These results along with spectrophotometric data prove the efficiency of bacteria suggesting their possible use in treating dye containing effluents. (C) 2010 Elsevier Ltd. All rights reserved.