Abstract: Random amplified polymorphic DNA (RAPD)technique was employed to detect the DNA polymorphism in 20 individuals of Coreius heterodon in the lower reach of the Yangtze River． 19 arbitrary primers were used and 90 repeatable RAPD bands were generated．The length of the fragments varied from 100bp to 1500 bp．The percentage of polymorphic fragments was 31.58% ，while the index of Shannon diversity was 0.1940．The genetic distance between individuals was from 0.0003 to 0.0976．Comparing the genetic diversity of Coreius heterodon with that of other fishes，the experiment revealed that the genetic diversity of Coreius heterodon in the lower reach of the Yangtze River was a little lower． Owing to lack of historic data，we could not judge the effect on its genetic diversity caused by excessive fishing and environment destruction according to the results of this research．