Introduction: Multidimensional and complex nature of children`s behavioral problems requires assessment and application of modern treatments. Therefore, this study was conducted to determine the effectiveness of attachment-based therapy on reducing symptoms of anxiety, loneliness, and self-esteem in orphaned boy children. Materials and Methods: This study was an educational trial with pre-test, post-test, and control groups. The statistical population included all orphaned boys living in institutional homes at Shahid Ghodoosi boarding center under the auspices of the Tehran Welfare Organization in 2019. By the available sampling method, 30 people were selected and divided into experimental (n=15) and control (n=15) groups. Then, they completed the Anxiety Inventory (Spence, 1999), the Loneliness Questionnaire (Asher et al, 1984), and the Self-Esteem Questionnaire (CoperSmith, 1976). In the experimental group, attachment-based therapy was conducted in 10 sessions, 1 per week for 1 hour. After the training, the groups were retested. Data were analyzed by t-test (independent and paired) and multivariate analysis of covariance. Results: The results showed the mean scores of the total anxiety, separation anxiety, social anxiety, obsession, phobia, and panic attack in the experimental group in the post-test phase to be significantly different from the control group(p<0. 05). There was a statistically significant difference between the mean score of loneliness and self-esteem of the subjects in the two groups in the post-test stage (p<0. 05). Conclusion: The study emphasizes the importance of attachment in orphaned children, potentially providing practical results for therapists to reduce the emotional-behavioral problems of orphaned children and adolescents.