Abstract: RAPD was employed to assess the genet ic variations among 6 Eriocheir sinensis and Eriocheir japonicus populat ions distributed in Liaohe, Yellow , Yangtze, Oujiang, Pearl and Nanliu River systems. ( 1) Two primers could amplify distinct ive bands in 48 polymorphic 10- mer primers. The 880bp band amplified by primer Z2 was characterized only by Pearl and Nanliu River populations, and the 700bp band was characterized only by Yangt ze, Yellow, Liaohe and Oujiang River populations, both bands can be used as fingerprint ing marker to identify E. sinensis and E. japonicus . (2) The frequency of 947bp band amplified by primer Opp17 declined from south to north, e. g. , Yangtze River population ( 87. 50%) , Yellow River population ( 41. 66% ) and Liaohe River population ( 10. 83% ) . ( 3) The average genetic similarity index within each population ranked as Liaohe River 0. 908> Nanliu River 0 . 897 > Oujiang River and Pearl River 0. 895 > Yellow River 0. 890> Yantze River 0. 850. The genetic distances and their UPGMA and NJ dendrogram of six populations indicated that there was an obvious divergence between Pearl River, Nanliu River populations in southern China and Liaohe River, Yellow River and Yangtze River populations in northern China.