The genetic differences of 15 mitten crab populations from 6 river systems in mainland China and 1 population from Russia were studied based on RFLP analysis of mitochondrial cytochrome oxidase subunit I(CO I).The results showed that Tas I-RFLP pattern could be used as a genetic marker to distinguish Eriocheir hepuensis from Eriocheir sinensis,Eriocheir japonica and Eriocheir leptognathus;genetic distances among 13 populations of Eriocheir sinensis range from 0 to 0.015,indicating that they were different geographic strains;the subspecies status of Eriocheir sinensis and Eriocheir hepuensis(population from Nanliujiang)were considered owning to their genetic distances of 0.02-0.044,indicating that genetic divergence between them was low;Eriocheir leptognathus(population from Nanpaihe,Tianjin)was the most distant taxon with genetic distances value of 0.147-0.195,which could be defined as genetic distances between species in genus Eriocheir. The genetic differences of 15 mitten crab populations from 6 river systems in mainland China and 1 population from Russia were studied based on RFLP analysis of mitochondrial cytochrome oxidase subunit I (COI). The results showed that Tas I-RFLP pattern could be used as a genetic marker to distinguish Eriocheir hepuensis from Eriocheir sinensis, Eriocheir japonica and Eriocheir leptognathus; genetic distances among 13 populations of Eriocheir sinensis range from 0 to 0.015, indicating that they were different geographic strains; the subspecies status of Eriocheir sinensis and Eriocheir hepuensis population from Nanliujiang) were considered owning to their genetic distances of 0.02-0.044, indicating that genetic divergence between them was low; Eriocheir leptognathus (population from Nanpaihe, Tianjin) was the most distant taxon with genetic distances of 0.147-0.195, which could be defined as genetic distances between species in genus Eriocheir.