Effect of Withania somnifera aqueous root extract on high cholesterol diet rats was investigated. Obesity was induced in rats by giving high cholesterol diet (coconut oil, grains, sugar, etc) for seven days in standard rat chow diet. The aqueous extract of Withania somnifera (100,200 mg/ kg body weight) was orally administered once a day to rats fed a high cholesterol diet for 30 days. High cholesterol-fed diet rats exhibited a significant  increase  in  total  serum  cholesterol,  triglycerides,  low-density  lipoproteins,  very  low-density  lipoproteins  and  a  significant decrease  in  high-density  lipoproteins.  Treatment  with  aqueous  extract  of  Withania  somnifera  significantly  decreased   total   serum cholesterol, triglycerides, low-density  lipoproteins,  very  low-density  lipoproteins  and  increased  the  high-density  lipoproteins  in  obese  rats and was comparable with that of standard Atorvastatin. After completion  of experiment rats  were  anesthetized with Isoflurane  and  sacrificed  and the atherosclerotic lesions  in  the aorta were  assessed. The obtained results of the investigation of all 5 groups were compared and found with significant inhibition of atherosclerotic plaque formation. Although a clear dose-dependent relationship was observed at the applied doses. Hence, it was concluded that significant anti-obese and atherosclerotic activities of Withania somnifera may be due to the presence of carbohydrates, tannins, phenols, flavonoids, proteins, amino acids and saponins found in the preliminary phytochemical screening.