Objective To evaluate the effect of elimination of schistosomiasis infectivity in water body by applying molluscicide on transmission marshland outside an embankment in Dongting Lake.Methods Two patches of transmission marshland with similar Oncomelania snails and infectious snails density in the northern part of eastern Dongting Lake regions were selected as molluscicide trail and control groups,respectively,and the snails and water body infectious indicators were investigated and compared between them.Results Adjusted death rate of snails in the trail group 15 days after applying molluscicide was 94.13%,without infected snails.The infection rate of sentinel mice in the trial group 50 days after applying molluscicide was 100.00%,with average 56.6 worms per mice.The infection rate of sentinel mice in the control group without molluscicide was also 100.00%,with average 147.8 worms per mice.Conclusions In transmission marshland areas outside the embankment of rivers or lakes,it is impossible for focus mollusciciding to eliminate the infectivity of schistosomiasis in water body,yet possible to reduce the degree of infectivity to a certain extent.