The effect of trapidil on experimental hyperlipemia and atherosclerosis induced by 1% cholesterol diet in SPF male rabbits (JW/KBL) was investigated by the determination of the lipid contents of the plasma and thoracic aorta and examination of morphological changes in the aorta. Trapidil inhibited the increase of total lipid (TL), total cholesterol (TC), free cholesterol (FC) and phospholipid (PL) by the cholesterol diet in all groups. The level of cholesterol (HDL-C) and phospholipid (HDL-PL) in high density lipoprotein (HDL) remained unchanged after the cholesterol diet and trapidil administration. The atherogenic index (TC-HDL-C/HDL-C, PL-HDL-PL/HDL-PL) was improved by the inhibition of TC and PL by the administration of trapidil. A morphological study of the aorta showed that trapidil inhibited lipid deposition. A microscopic observation of the intima by Sudan III stain showed that inhibition of lipid deposition corresponded with the quantity of trapidil administration. An observation of aorta using transmission electron microscopy (TEM) showed that trapidil inhibited the presence of form cells due to HCD. This inhibition corresponded with the quantity of trapidil administration; and no form cells were seen in the 50 mg/kg-administered group. An observation of intima using scanning electron microscopy (SEM) showed that trapidil inhibited the irregularly elevated regions by HCD. The structure of intima in the 50 mg/kg-administered group was similar to that of the control groups. The observation of the head angiogram showed that trapidil improved the stenosis in the lingual and temporal arteries which was caused by HCD.