The aim of this study is to investigate the effect of transcranial direct current stimulation (tDCS) of the brain, on the symptoms of obsessive-compulsive disorder.In this regard, 60 patients with obsessive-compulsive disorder at psychiatric ward of Arak Amir-Kabir Hospital, will participate. After explaining the study, in case of their consent, demographic information will be received, and those with a score higher than 20 on the Yale-Brown and other criteria for inclusion and exclusion will be enrolled. The subjects will be randomly divided into two intervention and control groups. The anode electrode will be placed in the left dorsolateral cortex (pF3 point; 20/10 EEG), and the cathode electrode will be placed in the lateral side of right contralateral orbit (p8 point; 20/10 EEG). Patients will receive electrical stimulation with 2 mA, for 20 minutes (8 weeks, 3 sessions per week). The results of Yale-Brown Obsessive-Compulsive scale will be recorded before intervention, at 4, 8 and 12 weeks throughout the intervention. In the control group, situation is the same; with the exception that there is no stimulation. All patients are on Fluoxetine 40-80 mg.