Abstract: The pearl oyster Pinctada martensii Dunker is the main species in Southern China Sea for commercial pearl production in Leizhou Peninsula and other Beibuwan Gulf regions.Observation on gonad of pearl oyster P.martensii with naked-eyes and sectioning the gonad,the hermaphrodite adults could be classified as two types:type A could be discriminated by observing the gonad and the affirmation of type B should puncture or section the gonad.The primary statistic results showed that the percentage of type A individual was 4.6% and type B was 3.4% in the specimen group, in which percentage of specimens reaching the bi-sexual maturation were 1.8% and 2.4% respectively.The self2fertilization and early embryonic development of these-types of hermaphrodites were studied by artificial dissecting2insemination in the seawater containing 0.07 ‰ ammonia.Observations on the early embryonic development indicated that self-fertilizing rate were much lower than those between dioecious individuals and many embryos were broken during developing stage while some embryos could develop to D-shaped larvae nonetheless.