Five sterols with a nucleus skeleton of 6-hydroxy-4-en-3-one, namely cholesta-6beta-hydroxy-4-en-3-one (1), ergosta-6beta-hydroxy-4,24(28)-dien-3-one (2), ergosta-6alpha-hydroxy-4,24(28)-dien-3-one (3), ergosta-6alpha-hydroxy-4,22-E-dien-3-one (4), and ergosta-28-methyl-6beta-hydroxy-4,24(28)-dien-3-one (5) have been isolated from the marine sponge Iotrochoto birotulata, collected from the southern China sea. Sterols 2-4 are new compounds, and 1 has been isolated from marine organisms for the first time. The structures have been elucidated on the basis of extensive spectroscopic and chemical properties.