The sterol compositions of the Pelecypoda, M. sultataria, S. sachalinensis, and the Gastropoda, H. discus hannai Inc, T. cornutus were investigated. The results areas follows: 1. The contents of the unsaponifiables and sterols of the Pelecypoda, M. sulcataria, S. sathalinensis, and the Gastropoda, H. discus hannai Ino, T. cornutus, are $12.0\%,;11.8\%,;and;16.2\%,;15.3\%$, respectively. 2. The complex sterols from the Pelecypoda and Gastropoda are well separated on Silica Gel HF 254 TLC impregnated with $15\%$ silver nitrate. 3. The prominent sterols of the Pelecypoda, M. sulcateria and S. sachalinensis, are 22-trans-24-norcholesta-5, $22-dien-3eta-ol$ $3.0\%;3.9\%$ 22-dehydrocholesterol $6.7\%,;10.2\%$, cholesterol $39.0\%,;48.6\%$ brassicasterol $14.1\%,;13.8\%$ 24-methylenecholesterol $19.4\%,;11.5\%$, stigmasterol $2.4\%,;0\%$ $eta-sitosterol;10.5\%,;11.9\%$, and fucosterol $4.3\%,;0\%$. 4. Abalone, H. discus hannai Ino, and T. cornutus contain cholesterol $98.0\%,=97.5\% as main component with small amounts of 22-dehydrocholesterol, brassicasterol and desmosterol. In H. discus hannai rno, 24-methylenecholesterot and fucosterol are also found.