Objectives : This study was to examined the degree of oral health knowledge, attitude of periodontal diseases and dental health behaviors and to examine the relationship among variables in 12-year-old adolescents. Method : Participants were 2,196 adolescents who live in Seosan with an average age of 12.2. Data was collected using a self administrated questionnaire from April 10 through June 10, 2011. Results : The knowledge of periodontal disease of the subjects was $2.46{pm}1.52$ and the attitude was $1.88{pm}1.11$. It appears that knowledge and attitude concerning periodontal and dental health among young Korean 12-year-old adolescents living in Seosan city are in need of improvement. The knowledge and attitude were significantly higher in high group than low group of income. The knowledge and attitude toward periodontal and dental health was positively related to dental health behaviors. Conclusion : Based on the findings, dental health behaviors are strongly associated with knowledge and attitude toward periodontal and dental health. This result suggest that the implementation of oral health promotion should be considered for various factors related to attitude of oral health in adolescents.