An epidemiological investigation on dental caries was undertaken with 810 children of nursery school, kindergarten, elementary and junior high school age in the town of Fuji, saga prefecture which is a mountain village with less movement of the population. From this investigation the following results were obtained regarding the dental caries prevalence and the status of treatment: 1. As for the dental caries prevalence of deciduous teeth, the dft index was 8.8 at age 3, whereas it was 10.7 at age 5. 2. As for the dental caries prevalence of the permanent teeth, the DMFT value was 7.7 at age 12, whereas it was 9.9 at age 14. 3. As for differences based on set, concerning the deciduous teeth, none was not recognized except for the caries prevalence indices at age 11 for the dft index, at age 6 and 11 for the dfs index, and at age 11 for the ft index. 4. As for differences based on sex, concerning the permanent teeth, none was not recognized except for the caries prevalence indices at age 5 and 9 for the DFT and DFS indices, and at 7 for the FT and F tooth rate. 5. There was a tendency toward as significant increase in dental caries in the deciduous teeth. 6. There was a tendency toward as increase in dental caries in permanent teeth from the commencement of eruption and rapid aggravation approximately from the upper grades of elementary school. 7. In the status of treatment of dental caries in deciduous teeth, the ft index was 4.1 at age 6. 8. In the status of treatment of dental caries in permanent teeth, the FT index was 4.5 at age 14. 9. There was no statistically significant difference among kindergarten and nursery school children except for the dft and dfs indices at age 4.