The sterol isolated from Rhodoglossum pulcherum was identified as cholesterol by mixed melting point of various derivatives with the corresponding derivatives prepared from authentic specimen of cholesterol. Furthermore, the identity was confirmed by X-ray diffraction analyses of the algal stenone and cholestenone. The authors also confirmed the existence of cholesterol in several red seaweed listed in Table I. Besides cholesterol, the authors isolated another sterol, chalinasterol from some algae. The discovery of cholesterol might be of some interest to biogenetic study of sterol, because cholesterol has been considered to exist only in animal sources.