Introduction. Oral health is one of the most important issues in public health. Most educational interventions, as the primary prevention strategy, are focused on increasing information and knowledge and are not usually effective. Therefore, the present study is aimed at determining the effect of theory-based education on oral health behavior and its psychological determinants including dental health literacy. Method. This randomized controlled educational trial was conducted in two girls’ high schools that were selected by multistage cluster sampling and were divided into an intervention and a control group. Literacy, knowledge, oral health behavior, dental plaque index, and constructs of the protection motivation theory were evaluated before and one month after four training sessions. Finally, the data were entered into the SPSS 19 software and were analyzed using the chi-square test, independent t -test, and Mann–Whitney test at the significant level of 0.05. Result. Before the intervention, there was no significant difference between the intervention and control groups regarding the mean scores of knowledge, behavior, and oral health literacy; plaque index; and protection motivation theory constructs. After the educational intervention, however, the means of these variables were significantly improved in the intervention group compared to the controls ( p < 0.05 ). Conclusion. The study findings were in favor of the effectiveness of the theory-based educational intervention in improving the knowledge, literacy, and behavior related to oral health. Yet, further research is suggested to determine the effectiveness of such an intervention in male students as well as in populations with different socioeconomic and cultural statuses.