Endometriosis is the growth of endometrial tissue in ectopic places outside the uterus. It affects 10% of women in reproductive age and is the major cause of infertility and gynecological problems. ...Siddha physicians claim that Vitex negundo leaf decoction reduces the symptoms in clinical practice. This study was carried out to find scientific evidence for the claim. The aim was to evaluate the effect of Vitex negundo aqueous extract on induced endometriosis in Sprague dawleyrats. Endometriosis was surgically induced in nulliparous female Sprague dawley rats with regular estrus cycle by auto grafting endometrium tissue on peritoneum. After 30 days of implantation, rats were allocated into two groups (n=6). Control group did not receive any drug, whereas test group received an oral dose of Vitex negundo aqueous extract for 30 days. After 30 days of treatment, the endometriosis cyst size and adhesion were measured and blood was collected for hematology. MDA and Thiol levels were estimated in blood as well as in cyst sample. Statistical analysis was done using unpaired t test by keeping P<0.05. The test drug significantly controlled the body weight gain (P=0.03), reduced adhesionby 40% (P=0.03), and reduced cyst size by 69% (P=0.05). The test drug significantly increased thiol in blood (P=0.03), as well as in endometriosis cyst (P=0.50), and also reduced the blood MDA level (P=0.001). Our study has created the scientific evidence for the siddha physician's claim on Vitex negundo by demonstrating increase in antioxidant and reduces inendometriosis cyst size, adhesion and oxidant levels.