(Dunker, 1861) is a commercial marine bivalve that is found in coastal waters of China, Japan, and Korea from the shallow subtidal to depths of 20 m. It has high nutritive and medical value according to traditional Chinese medicine. In addition, it is adaptable and has high growth rates and great market potential. Currently, this clam is only available from natural sources. Over the last few decades, however, overfishing and environmental pollution have caused dramatic declines in natural stocks of , and production is low and unstable. Fortunately, methods of artificial breeding and cultivation of the jackknife clam are developing. Previous studies on focused primarily on morphological and ecological characteristics, allozyme analysis, and evaluation of its nutrition components. Little is known about the molecular ecology of or its genetic background. Thus, it is important to evaluate genetic differences among populations along the coast of China. In this study, 14 microsatellite DNA markers were used to examine the genetic diversity and differentiation among five wild populations of the grand jackknife clam. A total of 150 samples were collected from Dandong (DD) in Liaoning Province, Qinhuangdao (QHD) in Hebei Province, Rizhao (RZ) in Shandong Province, Lyusi (LS) in Jiangsu Province, and Beihai (BH) in Guangxi Province. Comparisons of 199 alleles among the five populations showed that, in the fourteen loci, polymorphism information content (PIC)values ranged from 0.696 to 0.853 with high polymorphism. The number of alleles ranged from 8 to 22 and the average number () of alleles were 14.2 and 11.05, respectively. Expected () ranged 0.769–0.826 and 0.809–0.858, respectively, suggesting high levels of genetic diversity in all populations. Only the locus in the DD population deviated significantly from Hardy-Weinberg equilibrium, further indicating stability in the genetic diversity of all populations. The genetic distance among the five populations ranged from 0.141 2 to 0.340 9, with minimum and maximum distances between DD and QHD and between DD and BH, respectively. The UPGMA tree indicated highest similarity among geographically close populations, clustering DD with QHD and RZ with LS, the structure of which was confirmed by Bayesian cluster analysis. The were 0.039 1– 0.094 7, suggesting a moderate degree of differentiation among the five wild populations. Overall, the results suggest a high level of genetic diversity and differentiation among five grand jackknife clam populations from geographically distinct locations along the coast of China. Precaution should be taken to protect the germplasm of this species, particularly when designing stock enhancement programs.