The purpose of this study was to obtain the basic data provide continuous and active dental treatment for the mental handicapped children. The authors studied on the dental caries experience, oral hygiene slates and caries activity test in the mental handicapped children of 9-11 years old, who are housed by rehabilitation school in Kwang-ju and in the 30 normal children of 9-11 years old as a control group. Correlation coefficiency was calculated among the caries experience, oral hygiene states and caries activity test for every children. The obtained results are as follows. 1. The mental handicapped children showed remarkably high score compared to normal children in DMFT index(The Index score was $2.43{pm}1.98$ in the normal children and $5.26{pm}4.11$ in the mental handicapped.). 2. Correlation coefficiency was reveled very high score between DT index and DMFT index of the normal children(P<0.01), and the mental handicapped was also high score(P<0.01) between ft index and dmft index. 3. The PMA Index of the mental handicapped children was comparatively higher than the normal(The Index score was $4.03{pm}4.44$ in the normal children and $7.87{pm}7.33$ in the mental handicapped.). 4. In the correlation coefficiency between the caries experience and modified snyder test, DMFT index of the normal children was revealed some high score(P<0.05). DMFT index of the mental handicapped was showed remarkably high score(P<0.01).