Abstract: In the 50s' and 60s' shoals and marshlands with a high snail density and a large number of infective snails were widely distributed in the Yangtze River and the lakes in Jiangsu. The spreading of the snails from these areas to the surrounding and lower reaches was found to be serious.It was the main focus of acute schistosomiasis infections and closely related to the maintenance of schistosomiasis in the plain region with network of water ways. After more than twenty years schistosomiasis control, especially in the 70s', the distribution of the snail-infested areas was greatly reduced. However, the Yangtze River was flooding in recent two years, distribution of snail-infested areas was found to be extended as compared to the end of the 70s'. These shoals became very important in the epidemiology of schistosomiasis in Jiangsu. Because of the particular situation of the lower-readies of the Yangtze River and the serious spreading of the snails in these areas, much attention must be paid to these areas in Jiangsu Province for a long period of time.