Dyes which are discharged without being controlled reach to the human beings by food chain and threaten their health. 10-20 percent of synthetic dyes are discharged without being controlled to the waste waters after the dyeing process. In this study, the genotoxicity of synthetic direct ve dyes are searched by umu test (Salmonella thyphimurium TA1535/pSK1002) which is short term bacterial test system. Concentrations of 400 mu g/ml, 120 mu g/ml, 40 mu g/ml and 4 mu g/ml of dye solutions are prepared. By using S9 fraction, the biotransformation effects of the dyes in an organism at the presence of liver enzymes are researched. In this study, Direct Yellow 86, Direct Orange 39, Direct Blue 200, Direct Yellow 142 ve Direct Red 243 synthetic dyes are studied. At the end of the study, Direct Blue 200 have mutagenic effects at the presence of S9 fraction at 400 mu g/ml and 120 mu g/ml concentration also Direct Blue 200 has mutagenic effect at the absence of S9 fraction at 400 mu g/ml concentration.