In this study, cost and effectiveness were measured todetermine which approach is the most cost-effective amongthree approaches, namely, selective mass chemotherapy,molluscicide plus selective mass chemotherapy, andenvironmental change plus selective mass chemotherapy andmolluscicide, in reducing prevalence of schistosomiasis inthe marshland areas of south of China. This thesis is based on a field intervention study onschistosomiasis which was engaged in Anhui Province, southof China between 1982 and 1990 year. Three communities werechosen as study population. Before the implementation,prevalence was measured. Then, the people of the threecommunities were followed and examined annually during thewhole study period of eight years. The mass chemotherapy can drop the prevalence ofschistosomiasis from 20% to 5-7%. In the implementationperiod, chemotherapy is the most cost effective approach. Ifthe selective mass chemotherapy was stopped, the prevalenceof schistosomiasis would increase quickly. Molluscicde plus selective mass chemotherapy can dropthe prevalence of schistosomiasis from about 26% to 3-4%. Ifthe approach was stopped the prevalence of schistosomiasisincreased but at a slower rate than with selective masschemotherapy. In the long-term molluscicide plus selectivemass chemotherapy is an expensive approach. The environmental change plus molluscicide andselective mass chemotherapy can decrease the prevalence ofschistosomiasis closed to zero. In the implementationperiod, the investment in environmental change is expensiveapproach. But it takes very long time before theenvironmental change approach can decrease the-prevalence tolow level. For per unit time this approach is the mostcost-effective in three approaches.