About 200 kinds of marine algae grow in the ocean surrounding Japan. Moreover, a large amount of marine algae is cultivated domestically for use as foods and industrial materials. The production of marine algae was 639,210 t, amounting to ￥164,642 million in 1998. The marine algae used as foods consist of about 50 species, and the production was about 172,000 t in 1996. Japanese have eaten marine algae as a source of supply of minerals and vitamins. However, the dietary intake of marine algae is about 1/5 compared with that of fish. Recently, it has been suggested that the increase in the incidence of adult diseases in Japan, such as diabetes, hypertension, hyperlipidemia, etc. was caused by the decrease in the dietary intake of fish, shellfish and marine algae. The nutritional role of marine algae was examined and it was recognized that marine algae contribute to the prevention and treatment of various diseases. We also analyzed the effect of Undaria pinnatifida (Wakame) on the decrease of the concentration of serum and liver triacylglycerol in rats.