Traditionally Rheum ribes L. has been used in Iran as sedative and mood enhancer. This study investigated the efficacy and safety of a hydroalcholic extract of R. ribes in treatment of mild to moderate major depression disorder 33 patients were randomly assigned to receive either Rheum ribes hydroalcoholic extract (1200 mg/day) or placebo in a 6-week, double blind and parallel-group trial. Patients were assessed before the study and during weeks 1, 2, 4 and 6 by the Hamilton Rating Scale for Depression (HAM-D) and a score sheet on adverse effects. In week 4 and 6, the extract showed a significant superiority over placebo in reducing depressive symptoms. There was no significant difference between the 2 groups in terms of adverse effects. The results suggest that Rheum ribes hydroalcoholic extract has some anti depressive effects. However, further studies are needed to confirm these findings.