This is a double-blind randomized clinical trial which will start at June 2014 and end on June 2015 in Isfahan city. Serum insulin level is considered as a key variable and the sample size calculated 70 persons (35 persons for control group and 35 persons for patient group). Patient group will receive magnesium supplement (250 milligram) and the other group will receive placebo which is similar to the magnesium tablets in color, odor and appearance both for 8 weeks. All subjects will complete 4 physical activity and 4 dietary records. Outcome measurements including sex hormone levels, metabolic and inflammatory profiles will be measured at the beginning and end of the study as well as anthropetric measurements.

Inclusion Criteria:

• Having PCOS according to the Rotterdam criteria,
• Age between 20-45 years,
• Lack of pregnancy and lactation,
• Not having certain regime during last 3 months,
• Non-smoking,
• Not having diseases, including: diabetes, cardiovascular , hepatic, renal and thyroid,
• Not taking supplements,
• Being overweight (Kg / m 25 ≤ BMI)

Exclusion Criteria:

• Hormone Therapy,
• Pregnancy and lactation during the study,
• Severe weight loss (more than 2.5 kg per month) during the study