Chloroplast simple sequence repeat (cpSSR) technique was firstly used to study mating system of natural Pinus koraiensis population. Nine pairs of primers with clear spectrum bands, high stability and polymorphism were selected from 70 pairs of cpSSR primers to analyze the mating systems of 28 individuals. 14 polymorphic loci were detected in the nine pairs of primers. The multi-locus (tm) and single-locus (ts) outcrossing rate were 0.966 (SD=0.000) and 0.939 (SD=0.000), respectively, which were slightly higher than those of other tree species. The constant index (F=-0.035) was below zero, indicating the occurrence of excessive heterozygote. Moreover, inbreeding index (tm-ts=0.027; SD=0.000) was close to zero, indicating an insignificant inbreeding. MLDT analysis showed that multi-locus outcrossing rate differed from single-locus outcrossing rate in mating systems of 28 individuals, but the differences were not statistically significant.