Abstract: The finless porpoise Neophocaenaphocaenoides (G. Cuvier,1829) inhabits both in the coastal waters and Yangtze River and its adjacent lakes. It is protected in Order Ⅱ in China.The flipper of the finless porpoise is studied here in order to betterunderstand the origin and evolution of marine mammals. It is found that the basic structure of the flipper is similar to that of theother dolphins and porpoises, but some characteristics are worthy of notice. By making transparent skeleton in situ and X-ray photos, this paper gives detailed observation, measurement and analysis on four pairs of flippers. These finless porpoises werecaught in different time and location by the fishermen in Weihai by bycatch, and vary in age and sex. Compared with the previousresearch, transparent skeleton has its advantages of living, complete, clear, esthetical, precise and easy to observe. In addition, theX -ray photos can help to verify the result.The name, position, shape and size of each bone of the flipper are described in detailand the reason of lacking centrale and carple1has not been reported.Through further observation, it is found that the result showssome differences with others, for example, previous studies recorded theoverall shapeof the five carpuses is elliptical and thepha -langeal formula summarized 2-3, 5-9, 5-8, 3-4, 2-3. But the authors record the five carpuses and their cartilage forman irregular polygon, and the phalangeal formula is 0-1, 6, 5, 2, 0.The difference is likely to be associated with themethods, and it is very clear that more research is needed in order to better understand this.