Objective To study the mitochondrial cytochrome C oxidase 1(CO1) gene of Oncomelania snails from Miao River area in Hubei Province.Methods Oncomelania snails were collected from Miao River area, including upstream and downstream. Genomic DNA was extracted from the tissue of the snail. PCR was used to amplify a fragment of the CO1 gene. Sequences of the CO1 fragment were determined directly from the purified PCR products by an automated sequencer. Sequences for each individual were assembled and edited using ESEE 3 0 s. A distance matrix was computed using program DNADIST of PHYLIP(3 57). Unrooted maximum likelihood trees were calculated from program FITCH.Results The amplified CO1 gene of the snail was a fragment of 638 bp in length. Sequence analysis showed that the accumulated variable sites were significant different between upstream and downstream populations, being 29 and 46, respectively. From the number of variable sites in the gene,snails in this area were roughly separated into two groups. Each of them was a mixture of both upstream and downstream snails.Same haplotypes were confirmed to be present among the collected sites along the river. From the distance matrix of sequence divergence, the population upstream vs downstream differed by 0 0221?0 0105.Conclusion There were more variation in downstream population than that in upstream.Gene flow was identified in these populations. The phylogenetic trees suggest the existence of two groups,but all of them belong to O h hupensis .