The effect of education based on Health Belief Model (HBM) in decreasing dental plaque index among first grade of middle-school girl students in Hamadan SohrabiVafa M [1], Moeini B [2]*, Hazavehei SMM [3], Soltanian AR [4], Rezaei L [5] Received: 12 Aug, 2013 Accepted: 23 Sep, 2013 Abstract Background & Aims: Oral-dental health behaviors education to students is an important subject in the school to prevent dental problems. The use of suggested educational models and theories is a new way in health service fields. This study was done to determine the effect of health education based on HBM on the decreasing of dental plaque index among first grade of middle-school girl students in Hamadan. Materials & Methods: In this quasi-experimental study, 120 students were chosen through the stratified random sampling which were in 2 schools and 6 classrooms, and they were placed in the experimental (n= 60) and control groups (n= 60). Data collection tool was a questionnaire based on HBM constructs (perceived severity, susceptibility, benefits, barriers and self-efficacy), knowledge, dental health behaviors and determine dental plaque by disclosing agent. The educational intervention included 4 educational sessions of 60 minutes. Two months after intervention, two groups were followed, and the data were analyzed by using SPSS16. Results: There were no statistically significant differences in demographic factors in two groups. Significant differences were observed in perceived severity (P