Polycystic ovarian syndrome (PCOS) is considered to be one of the most common endocrine gynaecological disorders, and the majority of female affected by PCOS is increasing daily in women. In order to investigate the effect of Caesalpinia bonduc (L.) Roxb., seed extracts on letrozole-induced PCOS were studied in female albino rats. When PCOS induced rats were administered orally with Letrozole at a concentration of 1mg/kg/day dissolved in 0.5 per cent of Carboxy Methyl Cellulose (CMC) once daily for 28 days.The present study consisted of 42 female Albino rats and equally divided into seven groups. designated as (served as normal intact animals), vehicle control which was orally administered with CMC. The negative control group animals received Letrozole (Letroz). The positive control group animals received 20 mg/kg/day Pioglitazone and other groups received 100, 200 and 300 mg/kg/day of the aqueous seed extracts. The route of Letrozole led to abnormally in Biochemical parameter and histological analysis. C.bonduc was able to surely exert its defensive influence by give back hormone levels, with testosterone, estrogen and progesterone. PCOS rats treated with plant extract exhibited significant reduction in Triacylglycerides (TGL), Low-density lipoprotein (LDL), Very low-density lipoprotein (VLDL) and Total cholesterol levels, with an increase in High density lipoproteins (HDL) cholesterol.