Objectives: This study was to examined the level of psychosocial factors, dietary habits and DMFT index and to examined the relationship among variables in 12-year-old adolescents. Methods: Participants were 1,831 total students from 14 middle school who lived Seosan with mean age of 12.46 years. Data was collected using a self administrated questionnaire from April 13 to May 24, 2009. Psychosocial factors and dietary habits were measured using the 5-items and 10-items. A trained investigator made an oral examination of them in natural light using a mirror and explorer to determine their DMFT index. Data were analyzed with t-test, one-way ANOVA, and Tukey test, pearson correlation coefficient using the SPSS WIN 15.0 program. Results: Regarding dietary self-efficacy, perceived benefit and perceived barrier degree, the subjects achieved a mean of $3.89{pm}0.69$, $3.48{pm}0.63$ and $3.82{pm}0.63$ out of a maximum 5 points. And the dietary habit degree of subjects achieved a mean of $10.69{pm}4.02$ out of a maximum 20 points and the DMFT index were $1.91{pm}2.26$. Dietary habits was positively correlated with psychosocial factors and negatively correlated with DMFT index. And then perceived barrier score were negatively correlated with DMFT index. Conclusion: Based on the findings, dental caries experience is associated with perceived barrier and dietary habits. These results suggest that the implementation of health promotion should be considered for various psychosocial factors and dietary habits in adolescents.