As an index for evaluation of marine environmental pollution by spilled C heavy oil from the sunken vessel Nakhodka, we carried out mutagenic activity tests of several fishes. Some gave positive results in direct and indirect mutagenicity tests. The strength of the mutagenicity was not high compared with that of authentic mutagenic compounds, such as AF-2. Though fishes caught in the polluted sea area were not dangerous from the viewpoint of mutagenicity, continuous observation is required to guarantee the safety of sea food resources.