Purpose: The aim of this study was to investigate the effectiveness of transactional analysis group therapy on decreasing aggression in addicted couples. Method: The design of this study was quasi-experimental with a pretest–posttest control group design.The participants included 40 addicted couples from the camp of 'Life Expectancy' in Sabzevar.They were randomly assigned into two groups. The experimental group received 8 sessions of transactional analysis group therapy while the control group was not offered any intervention. Before and after the intervention, aggression questionnaire was completed by the participants of the study. Findings: The results of ANCOVA revealed that, in the post-test, the experimental group's aggression decreased significantly in comparison with that of the control group. The findings also confirmed that transactional analysis group therapy can reduce aggression in addicted couples.