Okayama Prefecture has been known as one of endemic areas of Clonorchis sinensis in Japan. In on attempt to see the chronological change in the area, several investigations have been conducted on the distribution of the parasite. 1. Parafossalurus manchouricus, the first intermediate host, was found in three cities and in two other districts, and the area of endemicity is seemingly less extensive than that reported by Nagano (1954). 2. The metacercarial stages were recognized in three cities and in a county being coextensive with the distribution of the snails. 3. The eggs in feces were recovered in both previous and present regions infested with the snails. 4. The avarage infection rate of liver flukes in the areas examined was approximately two per cent with an exception of seven per cent in Saidaiji City.