The genetic structures and variations of 16 enzyme loci in 8 populationsof silver carp,big head and grass carp from Chang Jiang River, Zhu Jiang River andHeilong Jiang River were analyzed by LKB horizontal acrylamide gel electrophoresis. Amarked biochemical genetic differences were found among different populations ofsame specics from different water systems. The mean proportion of polymorphic loci(P) was 13. 3%, 26. 7% and 13. 3%,the average heterozygosity per locus was 0 .0493, 0. 0484 and 0 .0511 for silver carppopulations from Chang Jiang River,Zhu Jiang River and Heilong Jiang River respe-ctively;For big head populations from Chang Jiang River and Zhu Jiang River,the Pwas both 31 .3%, but the H was 0.1375 and 0.0977 respectively;For grass carppopulations from Chang Jiang River,Zhu Jing River and Reilong Jiang River,the Pwas 30. 0%, 38. 0% and 21.3%, the H was 0.1241, 0.0961 and 0.0525 respectively.There was a trend that the mean prpportion of polymorphic loci in southern popula-tion was higher than that in northern population. The genetic similarity (S) of silver carps between Chang Jiang River and Zhu Ji-ang River,Chang Jiang River and Heilong Jiang River,Zhu Jiang River and HeilongJiang River was 0.9957, 0.9955 and 0.9696 successively;The S of big head popula-tions between Chang Jiang River and Zhu Jiang River was 0.9955; The S of grasscarp populations between Chang Jiang River and Zhu Jiang River,Zhu Jiang River andHeilong Jiang River, Chang Jiang Biver and Heilong Jiang River wax 0.9679, 0.9483and 0.9324 respectively. The genetic distance was smaller within the central popula-lions (Chang Jiang River and Zhu Jiang River),but was larger between the marginal populations(Heilong Jiang River) and the central population. The population size ofgrass carp in Heilong jiang River was very small, which should be given enoughaffention tco.