Abstract: The Regular Patterns of Mass Spectrometry of Sterols and Related Derivatives（Ｉ）. Mass Spectrometric Fragmentation Typicality of 5, 22-Dien-; 5, 24（25）-Dien-and 5, 24（28）-Dien　－Steryl Acetates—Steryl AcetatesZeng Zhi； Zeng Longmei　(Department of Chemistry, Zhongshan University, Guangzhou 510275, China)Xiang Tongshou　(National Laboratory of Organic Geochemistry,Chinese Academy of Sciences, Guangzhou 510640, China)Received 1993-05-25Abstract：Mass spectrometry plays a crucial role in the structure elucidation on new sterols,notably those from marine organism. Secure interpretation of the mass spectra requires　an adequate understanding of the mechanism of the key fragmentation processes of　steroids and the present paper summarizes the elucidation of the fragmentation 　mechanism of the most important peaks of the following classes of steryl acetates: （1） 5, 22dien - ;（2） 5, 24 （25）-dien - ; and （3） 5, 24 （28）-dien-steryl acetates. Attention is　drawn to the utility of such mass spectral decompositions in structure elucidation of the　marine sterols isolated from the South China Sea sponges.Keywords: marine sponge, sterol, mass spectrum