Sinojackia xylocarpa is a Chinese endemic species that is extinct in the wild but extant in botanical gardens. Microsatellites were used to investigate the genetic diversity and mating system of this species for future use in a reintroduction program. Ex situ conserved populations of S. xylocarpa maintain intermediate levels of genetic diversity (H_E=0.570–0.640). However, a general and significant heterozygote excess was found, with a mean F_IS of ？0.103. S. xylocarpa was determined to be predominantly outcrossing (t_m=0.992; t_s=1.092). Population size and genetic diversity were found to be positively correlated (r=0.991; P=0.084). Principal coordinate analysis (PCA) suggests that all extant individuals are derived from two source populations. Reintroduction strategies of S. xylocarpa were proposed on the basis of these results.