The influence of sediment contaminants on the Salmonella mutagenicity test was investigated to develop a preparation method not subject to interference by coexisting substances. Organic chemicals were extracted from sediment by dichloromethane/ethanol (4:1), acetonitrile or ethanol, and dichloromethane (DCM) extract was refined by washing with alkali, passing through a reduced-Cu column and/or fractionation with a silica cartridge. The strain Salmonella typhimurium TA98 was used. Sediment extracts and their refined preparations were first determined in their own mutagenicity, and then the influence on the mutagenicity of a fixed dose of 2-aminofluorene (2-AF) as a positive standard mutagen was examined. The toxicity to the strain was also tested. It was concluded that the coexisting environmental chemicals in sediment inhibited or promoted the original mutagenicity of the samples.