Decolorization of Basic Red 46 (Maxilon Red GRL) (BR46; azo dye) and Methylene Blue (MB.; cationic dye) was studied by using anaerobic sludge taken from upflow anaerobic sludge blanket bed (UASB) reactor treating wastewaters of Pakmaya Yeast Factory in Izmit, Turkey. Experiments were carried out under abiotic and biotic conditions. Abiotic tests were carried out without living biomass in order to determine color removal by non-biological process. The biotic tests were achieved at two cases as dye main carbon source without co-substrate (glucose) and using different concentrations of glucose (500-1000-1500-2000-3000 mg/l). For first case; the concentration of dyes was 25(B1), 50(B2), 100(B3) mg/l. In the other case; dye concentration was kept constant as 100 mg/l for changing glucose concentrations. MB removal (40%) was better than BR46 removal (25%) physically as physically in abiotic conditions. In biotic tests without glucose, color removal for both dyes were achieved at almost within in the 120 h. The maximum dye removal rates were obtained at the starting of experiments. In biotic tests with co-substrate, decolorizations rate of dyes was obtained faster than first case experiments. Almost complete removal for BR46 and MB were found in 25 and 50 h, respectively. The highest removal rates for both dyes were determined by co-substrate with the highest concentration of glucose, 3000 mg/l in the biotic conditions. BR46 and MB can be biologically degraded by using anaerobic sludge with and without co substrate. Decolorization of BR46 and MB was achieved at short time with presence of co-substrate.