Genotoxicity/mutagenicity of organic chemicals in industrial wastewater was investigated using umu-test with a Salmonella typhimurium TA1535 strain. The tester strain was derived by introducing plasmid pSK 1002, which carried a umu C - lac Z fusion gene into S typhimurium TA1535, and tester strain in the presence microsomal activation proved to be the more sensitive maker of genotoxicity. Genotoxic responses were observed in concentrated with a blue-rayon column, from 14 plants tested. The results were as follow; 1. Genotoxic responses were observed in concentrated from nine plants(64.3%) tested. 2. The results show that genotoxic activity was particulary high in the untreated wastewaters and decreased in the treated wastewaters(35.7%) 3. No significant correlation was found between genotoxicity and water ollution indicators, such as COD and BOD.