CA125 is a glycoprotein mucins (MUC16) tumor marker, used in screening, ovarian and endometrial malignancies and in monitoring therapy, early recurrences, and prognosis of these cancers. Hormonal induction for ovulation can elevate the risk of ovarian cancers so CA125 may be used for screening in PCOS as an unsafe group and the way of treatment may need to be changed in these patients. Polycystic Ovarian Syndrome (PCOS) is one of the most common hormonal disturbed diseases that can affect females in reproductive life. It has both metabolic and fertility impacts that can be seen in the reproductive period and post-menopausal life. To study the correlation between PCOS and CA125 level in relation to body weight in non-cancerous patients. 60 women were selected with age 18-42-year-old forty of them were diagnosed with PCOS according to Rotterdam criteria. They were divided into two groups according to BMI G1 was more than 25 kg/m 2 (overweight and obese) G2 was less than 25 kg/m 2 (normal) and the G3 was 20 healthy non-PCOS BMI less than 25 kg/m 2 . Blood samples were taken in the early follicular phase for assessing luteinizing hormone (LH), follicular stimulating hormone (FSH) and, free testosterone (FT) hormone. Other blood samples were taken at the late follicular phase to measure CA125 levels using Enzyme-Linked Immune Sorbent Assay (ELISA). PCOS G2 were significantly higher in the concentration of CA125 than PCOS G1 (p< 0.05), but there was no significant difference in CA125 level in groups when there is no significant difference in body mass index (BMI) between PCOS G1 and G2. P>0.05. The negative relation between CA125 concentration and weight. The tumor marker CA125 efficacy is decreased in obese women. Furthermore, PCOS not causes an increase in CA125 in the non-cancerous patient.