Abstract: Allozymic variation of five natural populations and one ex situ population of Eurycorymbus caraleriei (Levl.) Rehd.et Hand.-Mazz.was analyzed using isoelectric focusing in thin-layer polyacrylamide slab gels.Fourteen loci of seven enzyme systems were scored for the analysis of population genetic diversity and structure.A high genetic diversity was observed in this dioecious species,with mean number of alleles per locus A=1.6,mean percentage of polymorphic loci P=42.9% and average expected heterozygosity H_e=0.216.An excess of heterozygous genotypes was found in all populations,which resulted in a significant deviation from the Hardy-Weinberg (equilibrium).The low value of the relative magnitude of genetic differentiation among populations (G_st=0.069) suggests little genetic differentiation and a sufficient gene flow (N_m=3.128) occurred among natural populations.UPGMA cluster analysis using Nei’s (1978) unbiased genetic distance revealed that the ex situ population was firstly clustered with Shimen population,suggesting the ex situ collection is probably form Shimen population.Although the gene diversity in ex situ collection was found for accounting for about 85% of the total genetic variation in the species,genotype diversity retained in ex situ collection only covered about 16% of the total of the species.As the result,we strongly recommend that more genotypes should be collected from natural populations to maintain the genetic integrity of the species in ex situ collection.