This study examined the effect of dietary fucoxanthin or fucoxanthinol on the amount of docosahexaenoic acid (DHA) in the liver of KKAy mice, a model for obese/type II diabetes. In the first experiment, mice were fed diets containing crude fucoxanthin or glyceroglycolipid for 4 weeks. Results showed a significant increase in the level of DHA in mice fed 0.53% crude fucoxanthin, from 2.3% in control mice to 5.1% of fatty acid composition of total liver lipids. On the other hand, in mice fed crude glyceroglycolipid, the level of DHA as a proportion of total liver fatty acids remained unchanged. To clarify the enhancement of hepatic DHA, in the second experiment, KKAy mice were fed a diet containing purified fucoxanthin or its deacetylated derivative, fucoxanthinol. Results from a quantitative analysis using an internal standard showed that in mice fed 0.2% fucoxanthin, the amount of hepatic DHA was 2-fold higher than in control mice, whereas DHA levels in the small intestine remained unchanged. Furthermore, 0.2% fucoxanthinol led to 1.8- and 1.2-fold increases in the amount of hepatic DHA and arachidonic acid compared to control mice, respectively. These results indicate for the first time that dietary fucoxanthin and fucoxanthinol enhance the amount of DHA in the liver of KKAy mice.