The purpose of study was to test the hypothesis that preschool children who experienced nursing caries have high dft index and caries activity in primary dentition. One thousand and seventy-five preschool children from 4 to 6 years old were examined for their caries experience and salivary invertase activity by Resazurin Disc Test. Nursing caries group was identified by the criteria of having more decayed and filled teeth among the upper incisors than among the upper molars. The prevalence of nursing caries was 15.8%. The dft index of nursing caries group was significantly higher than that of the other groups except the rampant caries group(P<0.01). The Resazurin Disc Test score of nursing caries group was significantly higher than that of the other groups(P<0.01) and there was no difference between nursing caries group and rampant caries group. Therefore, it is recommended that children who experienced nursing caries should be incorporated in the caries prevention program through the primary and mixed dentition.