This study was performed to investigate the induction of experimental atherosclerosis in rats and inhibitory effects of aloe vera on progression of atherosclerosis in rats. A dose range finding study of cholesterol and vitamin D₂ for the induction of atherosclerosis and studies on the subchronic effect of aloe vera and on the chronic effect of aloe vera were carried out. A total of 3-week old 125 male rats of Sprague-Dawley were divided into 25 groups and fed with the diet containing cholesterol (0.1, 0.2, 0.3, 0.5, 1.0 and 2.0%) and vitamin D₂ (500, 5000, 50000 and 500,000 IU/100 g) for 4 weeks. 35 male rats were divided into 7 groups and fed with the diet containing aloe vera with 1.0% of cholesterol and 50,000 IU/100 g of vitamin D₂ for 4 weeks. 200 male rata were divided into 5 groups and fed with cholesterol and vitamin D₂ for 6 and 12 months. Growth, clinical and pathological changes of rats in the three experiments were observed. The results were as follows: 1. In the dose-range finding study, feed intake, feed efficiency ratio and weight gain were significantly decreased and relative liver, heart, kidney and stomach weight to body weight were increased in all of the feed groups containing 500,000 IU/100 g of vitamin D₂. Serum biochemical values of total cholesterol, high-density lipiprotein cholesterol (HDL-cholesterol), triglyceride, calcium, inorganic phosphorous and chloride of male rats in treated groups. The aorta and coronary artery of rats in all of the diet group containing 500,000 IU/100 g of vitamin D₂ showed typical atheroaclerotic lesions. 2. Male rats fed with the diet containing aloe vera with 1.0% cholesterol and 50,000 IU/100 g of vitamin D₂ for 6 and 12 months did not show significant difference of diet intake and weight gain, and relative organ weight. The level of serum HDL-cholesterol and triglyceride recovered to the normal range by the aloe vera ingestation. 3. The aorta showed irregular appearence in the tunics intima with swelling, necrosis and calcification. The aorta of rat fed aloe vera diet showed no pathological lesions such as atherosclerosis of aorta. Aloe vera could have a helpful effect of vitamin D₂ and cholesterol induced atherosclerosis in rats. Long-term supplementation of aloe vera may slow down the process of experimental atherosclerosis in rats have effects on the development of atherosclerosis.