Abstract:Mating system is an important factor affecting the genetic structure of plant populations. Determining mating system can aid in the understanding of reproductive patterns of plants, and help predict the trend of genetic structure of plant populations following environmental change, such as habitat fragmentation. Ardisia crenata var. bicolor, a hermaphrodite species, is an understory shrub of evergreen broad-leaved forests in East China. Three polymorphic loci (Adh-1, Fe-2 and Amp-2) were analyzed to determine the mating systems of two A. crenata var. bicolor populations. Multiple loci outcrossing rates of the two populations were 1.055 and 1.159, respectively. This may represent a combination of several small groups into large populations as a small number of families in groups can not be used to calculate the multilocus outcrossing rate. Low outcrossing rates were found in families of small groups but not in those of large groups, indicating that outcrossing rate will be reduced with small population size or low density of flowering plants. We discuss the effects of fragmentation of evergreen broad-leaved forests on the mating system of A. crenata var. bicolor populations.