Sexual system, ovule development and abortion of selfpollinated fruits in Xanthoceras sorbifolium were investigated through direct observations, light and scanning electron microscopy to understand why a very small proportion of flowers give rise to mature fruits, based on the samples of male and bisexual flowers in different developmental stages. The results indicated that: (1) the plant bears a large proportion of male and a limited number of bisexual flowers and exhibits cryptic monoecy. (2) There are five unique golden hornlike appendages in a flower. Mature pollen grain is spheroidal, tricolporate and parasyncolporate, with verrucate ornamentation. The flowers are mainly windpollinated. (3) The dry stigma is trilobed and the surface is densely covered with filiform papillae at anthesis. (4) The ovoid and amphitropous ovule contains a long curved embryo sac that is embedded within the massive nucellar tissue. After fertilization, a radially stretched bulge is produced by local periclinal and anticlinal divisions of the outer integument between the micropyle and the chalaza at the raphal side, which extends into the embryo sac perpendicular to its longitudinal axis. The fertilized embryo sac forms a sink into which water and soluble materials are draw. Two cotyledons of the young embryo reach the vesicle of the chalazal end of the embryo sac by growing along the neck of the micropylar end of the embryo sac. (5) In the early development of the embryo, the twin cotyledons are symmetrical. The cotyledon having the longer radium of curvature becomes much larger than the other cotyledon after 35 days after pollination (DAP). The liquid content of the vesicular embryo sac contains free nuclear endosperm and a slight amount of cellular endosperm before 23 DAP, during which the fresh ovules are edible. (6) Postzygotic abortion of selfpollinated ovules and young fruits occurs at various stages of development. The studies indicated that many sexual reproductive features of X. sorbifolium are shared with other members of Sapindaceae，but the plant is characterized by some unusual features in the family, such as occurrence of floral appendages and large ovule number per locule.