Background & objectives: Evidence suggests that there is a prevalence of sedentary lifestyle in children and adolescents. To design and implement interventions for increasing physical activity in adolescents, it is necessary to determine factors influencing physical activity in this age group and prevent inactivity. Therefore, the present study aims to determine factors influencing physical activity in Bushehrian school girls based on health promotion model.Methods: In this cross-sectional study, 410 girl students in first secondary schools in Bushehr were evaluated with cluster sampling. The questionnaire consisted of three parts: Demographic, questions related to health promotion model (perceived benefits, perceived barriers, self-efficacy, social support, and activity related affect) and International physical activity questionnaire (IPAQ). For data analysis, descriptive test, Chi-square, ANOVA and logit regression model were used.Results: The students in terms of physical activity were divided into three categories, 40.2% (n =165) of students were inactive, 40.5% (n=166) minimally active and 19.3 (n=79) HEPA active. physical activity status was not associated with personal factors such as age, body mass index (BMI), job and education. While the prior physical activity had a significant association with physical activity behavior (p<0.001). All health promotion model constructs had a significant association with physical activity. The results indicated that physical activity was predicted by perceived benefits (b=0.015, p=0.036), perceived family support (b=0.015, p=0.014) and prior physical activity (b=1.008, p=0.000).Conclusions: Family support is one of the most important factors for influencing physical activity, therefore motivating family members for student support and training benefits of physical activity in student especially in student without prior physical activity can be an effective step to promote physical activity in this group of people.