Mutagenicity of fucoxanthinol (FXOH), the major compound after oral ingestion of fucoxanthin (FX), was evaluated by in vitro Ames test, and of FX by in vivo micronucleus test. In in vitro Ames test, bacterial reverse mutation was examined by using Salmonella typhimurium strains TA98, TA100. TA1535 and TA1537, and Escherichia coli Wp2uvrA/pKM101, with or without metabolic activation by S9 mix in the preincubation method, and mutagenicity of FXOH was found to be negative in all cases. In in vivo micronucleus test, mice were orally administered with FX at doses of 500, 1,000 and 2,000 mg/kg, and the bone marrow cells were taken 24 hr after the administration to observe the incidence of micronucleus cells, and mutagenicity of FX was found to be negative at all doses. Based on the data of the present Study it can be presumed that orally administered FX is a safe compound in terms of mutagenicity under the experimental conditions employed here.