PURPOSE: To obtain a new sterol compound having excellent antineoplastic activity, useful as a medicine, etc., by chemical modification of aragusterols extracted and isolated from a sponge belonging to Xestospongia.

CONSTITUTION: This new sterol compound of formula III having excellent antineoplastic activity and useful as a medicine, etc., is obtained by chemical modification of aragusterol A of formula I or aragusterol D of formula II each extracted and isolated from a sponge belonging to Xestospongia gathered at the coral reef in the sea near Iriomote Island, Okinawa prefecture, Japan. This compound is obtained by reducing the aragusterol A of formula I or the aragusterol D of formula II with sodium borohydride in an alcohol followed by oxidation in methylene chloride in the presence of disodium hydrogenphosphate and m-chloroperbenzoic acid.