Background: Adolescence is a period of heightened “roller coaster", where changes in self-esteem develop gradually in a discontinuous manner that increases the self-consciousness and anxiety over how individuals perceive each other. Aim: This study aimed to evaluate the effect of school-based intervention on social phobia and self-esteem among adolescent girls. Design: Quasi-experimental research design was used in this study. Setting: This study was conducted at Gamal Abdel Naser governmental secondary school for girls at Zagazig city, Al-Sharkia Governorate. Subjects: A purposive sample of 260 students were selected randomly and enrolled in the assessment phase. Then the intervention was carried out on 187 participants based on the assessment phase's result. Tools: Three tools were used in this study: Socio-demographic data sheet, Social Phobia Inventory (SPIN) and Rosenberg self-esteem scale (RSES). Procedure: A school-based intervention program was developed by the researchers and implemented to the experimental group. Participants were divided into six groups; each group consisted of 30-35 girls. The program consisted of 12 sessions and was implemented during school day, twice daily, three times per week, one session for each group every week for three months. Post assessment was carried out through completing SPIN and RSES during the last session. Results: More than two thirds of surveyed students experienced different levels of social phobia symptoms and about one fourth of them had low and moderate self-esteem levels. After intervention, participant student showed significant reduction in social phobia symptoms and improvement in self-esteem levels. Significant negative correlation was found between social phobia and self-esteem before and after intervention. Conclusion: School-based intervention for adolescent girls was effective in reducing social phobia symptoms and improving self-esteem levels. Recommendations: There is a great need for continuous follow-up of the participated students in the school-based intervention program to support and boost their coping strategies with anxious- feared social situations as well as their self-esteem.