BackgroundThe imprisoned women usually have low self-esteem and suffer from various physical and mental complaints; they may suffer from feelings of emptiness, isolation, and depression. Transactional analysis (TA) is part of a comprehensive system attributed to the individual and social psychiatry for personal development of self-esteem among the imprisoned women. Therefore, the present study aimed to investigate the effect of TA group-training on the self-esteem of imprisoned women.MethodsThis clinical trial was conducted among the imprisoned women in a prison in Southeastern Iran using pretest-posttest design. In this regard, 76 women were randomly allocated to the intervention (n = 35) and control (n = 41) groups. The TA group-training program was held for eight 90-min sessions for the intervention group. Data were collected using a demographic questionnaire and the Rosenberg’s self-esteem scale (RSES). Later, all participants were evaluated before and 1 month after the intervention.ResultsIn pre-test, the mean scores of self-esteem were 11.8 ± 4.67 and 7.97 ± 4.52 for the intervention and control groups, respectively. These scores showed low levels of self-esteem and the difference between the two groups was significant (p = 0.001, t = − 3.61). In the post-test, the mean scores of self-esteem improved to the moderate level (22 ± 2.52) in the intervention group compared to the control group (8.92 ± 4.04). This indicates the significant improvement of self-esteem in the intervention group (p = 0.001, t = 17.15).ConclusionsThe results showed that TA group-training had a significant effect on self-esteem. Therefore, the experienced and expert counselors and psychologists are recommended to hold transactional analysis group-training courses to enhance self-esteem among women prisoners.Trial registrationIranian Registry of Clinical Trials, IRCT20170725035289N5 Date registered: 25/08/2018.