Neuromodulation techniques for the treatment of Obsessive-Compulsive Disorder (OCD) have expanded with the greater understanding of the brain circuits involved in this disorder. Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that has been studied as an alternative for strategy for treatment-resistant OCD. The main study is a randomized, sham-controlled, double-blinded trial tDCS for OCD patients unresponsive to cognitive-behavioral therapy and/or selective serotonin reuptake inhibitors. Forty-four patients will be randomized to two groups: active or simulated intervention. The intervention consisted of delivering an electric current of 2mA to the cathode, positioned bilaterally in the cranial region corresponding to the supplementary motor cortex, and the anode positioned in the deltoid (neutral region), during 30-minutes, for four consecutive weeks. The primary outcome was the reduction in baseline YBOCS scores before and after of tDCS treatment. Secondary outcomes include measures of depressive and anxiety symptoms, genetic markers, motor cortical excitability and performance in neurocognitive tests.