Obesity is a universal health concern that can lead to serious diseases. The side effects of synthetic anti-obesity drugs necessitate the finding of suitable natural/herbal alternatives. Mother nature offers a wide range of plants with medicinal properties that include crude extracts and isolated compounds which are effective for controlling and reducing weight gain. Obesity was induced in 60, 3-week-old male ICR mice, using high-fat diet (60% dietary energy from fat) for 16-week. The mice were divided at random into six groups with 10 mice: mice fed with high-fat diet (HFD) only, mice fed normal diet only (NC), and orlistat at 15.9 mg/kg (HFD+Orlistat), and mice in three other high-fat diet groups treated with methanolic leaf extract of Clinacanthus nutans (MECN) at 500, 1000 and 1500 mg/kg. After 21-day of the treatment, MECN significantly reduced (P<0.05) the body weight, visceral fat and muscle saturated fatty acid compositions. There was also significant downregulation of HSL, PPAR α and PPAR γ and SCD genes expressions in the obese mice treated with 1500 mg/kg MECN compared to the HFD group. Therefore, MECN is a potentially useful natural supplement for alleviating obesity and obesity-mediated metabolic diseases.