Levels of sterols including ${Delta}^7$-dehydrogenase isolated from the tissues of marine animal products (20 species) were determined on 1.5% OV-17 columm of gas-liquid chromatography. The composition showed that the mussels and clams contained various sterols in their tissues : cholesterol, brassicasterol. 24-methylenecholesterol with some minor components such as 22-trans-norcholesta-5,22-dien-3${eta}$-ol, 22-cis-dehydrocholesterol, 22-trans-dehydrocholesterol, desmosterol, 7-dehydrocholesterol, campesterol, stigmasterol, ${eta}$-sitosterol, isofucosterol, and 7-dehydrocholesterol which could be converted into vitamin $D_3$ in the skin tissue of animal was present in the muscle of oyster, Crassostrea gigas. On the other hand, the others including gastropoda were predominantly composed of cholesterol. The minor sterols such as 24-methylenecholesterol, stigmasterol and ${eta}$-sitosterol in the fish intestines are supposed to be derived from dietary plankton. Cholesterol ${Delta}^7$-dehydrogenase which could convert cholesterol into ${Delta}^7$-dehydrogenase was present in the pickles of Tricurus haumela intestine.