Quantitative study of behavior should be preceded by precise description and definition of behavior. Therefore, an ethogram, which includes the comprehensive descriptions of the characteristic behavior of a species, should be constructed before any behavioral and behavior related study on the species. Although it has been started since 1970s' the behavioral studies on the Yangtze finless porpoise were generally unsystematic and descriptive. In order to develop an ethogram of the species for further behavioral and other studies, the behavior of three captive Yangtze finless porpoises, one adult male, one adult female and one sub-adult female, were observed and analyzed. Two months of preliminary observations were carried out between December, 1999 and January, 2000, aimed at obtaining a basic understanding of both the subjects and the behavior of them. The observations were made day and night, from the tank side above the water surface, mainly following the focal animal sampling protocol. Between May and July, 2000, ad libitum diurnal recording of the underwater behavior of the animals were made through video taping. After analyzing the record of the above observations, systematic focal animal sampling on the behavior of the animals across the 24 hr cycle were performed during December, 2000, from the tank side above the surface. Approximately forty behavior patterns of the animals were defined. According to the appearance and possible function of the behavior, the ethogram for captive Yangtze finless porpoise was constructed. The ethogram was composed of eight general behavioral categories, i.e. aerial display and surface behavior I play, begging food, socialization, sexual behavior, resting, rubbing, and miscellaneous. Even though possibly incomplete, the ethogram is likely to provide a valuable basis for further study on the Yangtze finless porpoises. Possible biological significance of some behaviors was discussed.