Abstract: Electrophoretic techniques have been used to survey five different field-collected isolates (i.e.,Anhui,Hubei,Guangxi,Sichuan and Yunnan) of S.japonicum from the mainland of China for genetic variation at 7 isozymes markers representing 9 loci.Polymorphic loci were observed for LDH-1,LDH-2,MDH and PGM,respectively,the proportion of polymorphic loci being 44.4%.Average heterozygosity varied between 0.223 and 0.425,with a mean of 0.332.Nei's genetic distance (D) among the populations of 5 isolates gave values between 0.001 and 0.039 with an average of 0.023,indicating that these isolates are very closely rehted.