Abstract: Quantitative study of behavior should be preceded by precise description and definition of behavior1Therefore,an ethogram,which includes the comprehensive descriptions of the characteristic behavior of a species,should be constructed before any behavioral and behavior related studyon the species1Although it has been started since 1970s’,the behavioral studies on the Yangtze finless porpoise were generally unsystematic and descriptive1Inorder to develop an ethogramof the speciesforfurther behavioral and other studies,the behavior of three captive Yangtze finless porpoises,one adult male,one adult female and one subadult female,were observed and analyzed1Two 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 them1The observations were made day and night,fromthe tank side above the water surface,mainlyfollowing the focal animal sampling protocol1Between May and July,2000, ad libitum diurnal recordingof the underwater behavior of the animals were made through video taping1After analyzing the record of the above observations,systematic focal animal samplingon the behavior of the animals across the 24 hr cycle were performed during December,2000,fromthe tank side above the surface1Approximatelyforty behavior patterns of the animals were defined1According to the appearance and possible function of the behavior,the ethogramfor captive Yangtze finless porpoise was constructed1The ethogramwas composed of eight general behavioral categories,i1e1aerial display and surface behavior,play,begging food,socialization,sexual behavior,resting,rubbing,and miscellaneous1Even 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