Introduction: This project studied the direct and indirect impact of social self-efficacy on loneliness of adolescents. Method: In this descriptive and cross-sectional study the selected samples were 946 students (471 girls and 475 boys) of high schools from north, east, west and central regions of Tehran. Participants completed children self-efficacy questionnaire, social avoidance scale, Peer rejection questionnaire and child social support questionnaire. Data analyzed by SPSS AMOS software. Results: Direct impact of social self-efficacy on loneliness was significance and indirect impact of social self-efficacy on loneliness was significant by social anxiety and social support. Conclusion: Social anxiety and social support affect the social self-efficacy on loneliness directly and indirectly. So, in prevention of damage of loneliness in adolescents, social self-efficacy and its dependent variables are important.