Introduction: The aim of this study was to determine the effectiveness of cognitive therapy on depression among the adults with stuttering.Materials and Methods: This was a quasi-experimental study with pretest-posttest design and control group. The statistical population included all adults referred to speech therapy clinics in Karaj City, Iran, in 2016; among them, 40 respondents diagnosed with depression were selected via available sampling and randomly assigned in experimental and control groups. The depression level was assessed among all the patients using the Beck Depression Inventory (pretest). Interventions were administered based on cognitive therapy in 10 sessions for the experimental group. At the end of intervention, all the participants were assessed again for depression level (posttest). The data were analyzed via SPSS software using ANCOVA test.Results: Comparing the mean pretest and posttest scores in both the experimental and control groups, the mean posttest depression score decreased significantly in experimental group (P < 0.010).Conclusion: Our results provide the evidence to suggest that cognitive therapy is an excellent method for treatment of depression in adults with stuttering. In addition, regarding the effectiveness of intervention, it can be widely used for treatment of mental disorders in clinics.