Geochemical investigation of river waters and reservoirs in Seoul city on fluorine contents were conducted between June in 1969 and February in 1970. Fluorine contents of most river waters and reservoirs in Seoul city were between 0.09 and 0.32 mg/l. It was found that fluorine contents of Han River and rivers running through the outskirt of the city were relatively less than those of the river waters running through the residential areas and the industrial areas. Fluorine contents were less seasonally variable than chlorine ones. Some implications of those results were discussed in detail.