Introduction: This study was aimed to investigate two kinds of treatment in patients with Irritable Bowel Syndrome and compare their efficacy on improving patients’ symptoms and their mental health one with just medical treatment and another with a combination of psychotherapy and medical treatment..Method: In a quasi-experimental study, 50 IBS patients were chosen among patients who came to a Gastroenterology Clinic. They were physically evaluated using ROME-II and mentally evaluated using SCL-90-R and then randomly appointed to two groups: medical treatment group as the control group and the combination of medical and psychological treatment as the case group. The subjects at the case group received cognitive behavioral psychotherapy for 8 sessions. Then, both the case and the control groups were evaluated using ROME-II and SCL-90-R. The data were analyzed using t test and U Mann-Whitney test for independent groups. .Results: The findings of this study showed that a combination of cognitive behavioral therapy and medical treatment is more effective than medical treatment alone in alleviating IBS symptoms. The mental health of the case was meaningfully better than that of the control..Conclusion: Considering the role of cognitive behavioral therapy combined with medical treatment in IBS patients, we recommend that a team of gastroenterologists and psychologists manage such patients.