The prophylactic effectiveness of Moclobemide in Chronic Tension Type Headache was studied in 21 patients (mean age 39.33 ± 8.53). They were diagnosed by International Headache Society diagnostic criteria. They didn't have depression, revealed by Hamilton's depression scale and clinical examination. We recorded P300, before and 4 weeks after the treatment for evaluating the cognitive effects of the drug. After the treatment of 10.05 ± 5.8 weeks, 38 % had no headache, 43 % had nearly complete remission, 14 % had minimally decreased headache and 5 % had headache just as before the treatment. P300 parameters weren't affected by the treatment. As a result in this study, Moclobemide is one of the good alternatives of prophylactic treatment of Chronic Tension Type Headache