Abstract: Nine populations of Oncomelania,field collected from Anhui,Shanghai ,Jiangsu,Zhejiang,Jiangxi,Hunan,Hubei,Sichuan and Yunnan were studied by horizontal starch gel electrophoretic method with 24 enzyme systems(AAT,AcPH,AK,AO,APH,CK,EST,GDH,GPI,G6PD,HBD,ISDH,LAP,LDH,ME,MDH,MPI,NADD,OCT,PGM,6PGD,SDH,SOD,XDH)analyzed.40 loci and 117 alleles were detected in the Oncomelania.Both of GPI and PGM Ⅰ,with 7 alleles,were the most variable loci.22 loci had more than 3 alleles each.Of 40 loci examined in the 24 isozyme systems,14 were found to be polymorphic,the proportion of multilocus enzymes being 58.3%.Our results showed that the genetic polymorphism existing in the populations of Oncomelania in the mainland of China.PGM and MDH,were found in both the populations of Oncomelania and strains of Schistosoma japonicum in the mainland of China.The results provided a new idea for studying snails and Schistosoma.Also,we found that there might be some correlation between the polymorphic locus and the feature of the shell of Oncomelania snail.