Fluoridation of public water supply in Fangcun Guangzhou was carried out from 1965 to 1983. Data of dental caries of children aged 3-6 in Fangcun and other statistical data were in May 1986 and January 1988, which were 31 months and 52 months respectively after stopping water fluoridation in October 1983. Compared with that during the water fluoridation, the result of survey in 1986 showed that prevalence of dental caries and other statistical figures increased significantly (P less than 0.01) in the 3-year-old group, but non-significantly in the groups of children aged 4-6 because they were born during the water fluoridation period. The result of survey in 1988 demonstrated significant increase of dental caries in the groups of children aged 3-5, particularly the interdental caries of front teeth which went up most noticeably, but non-significantly in the 6-year-old groups for the same reason. The results confirmed that systemic effects of fluoridation were more important and the prevention of interdental caries was best in water fluoridation programs.