Premenstrual syndrome (PMS) is one of the commonest painful problems during reproductive age among women with associated symptoms occurring before menstruation, which affects their personal lives and causes them to miss work. Some clinical trials have revealed the effects of Matricaria Chamomilla (MC) on such pains. In the present randomized, double blind, parallel -group study, we compare the effects of MC Extract and Mefenamic Acid (MA) on the intensity of PMS. In doing so, 90 students of Kazerun Islamic Azad University living in the dormitory are enrolled in the study. Participants undergo a preliminary screening interview and screening for depression using Beck questionnaire. Then, the eligible ones complete daily form for the severity of PMS for two consecutive cycles. Those diagnosed with varying intensity, are randomly divided into two groups each receiving one 100 mg capsule of MC or MA 250 mg three times daily from 21st day of menstrual cycle till the beginning of the next. Inclusion criteria are as follows: Single students of 18-35 years of age, with regular menstruation and confirmed diagnosis of PMS but without any physical or psychological diseases, using no hormonal drugs, vitamins and herbal ones. Exclusion criteria include sensitivity to drugs, incorrect use of capsules, specific disease and taking medications during the study. The main Outcome measures including severity of psychological, physical and total symptoms of PMS are assessed before (two screening cycles) and after treatment (two treatment).