Hypercholesterolemia is one of the major risk factors that precipitate coronary heart disease and atherosclerosis. In the present study, the effect of flaxseed oil supplementation on serum lipid profile, apolipoprotein A (apo A), apolipoprotein B (apo B), Lipoprotein a Lp(a), homocysteine and endotheline-1 (ET-1) in high cholesterol diet-induced hypercholesterolemia in rats have been evaluated. This study was carried out on 60 male rats. The rats were divided into four equal groups of 15 rats each. Group Ι :( Control group): rats fed on normal diet. Group Π: Rats fed with hypercholesterolemic diet (HCD) [4% cholesterol (w/w) and 1% cholic acid] and received no drug all over the period of the experiment. Group III: Rats fed with HCD + administrated flaxseed oil (270 mg/kg, body weight/day orally) after two weeks from induction of hypercholesterolemia. Group IV: Rats fed with normal diet + administrated with flaxseed oil (270 mg/kg, body weight/day orally) after two weeks from the onset of the experiment. Blood samples were collected from all animal groups three times at 2, 4 and 6 weeks from the onset of treatment with flaxseed oil. The obtained results showed that, cholesterol-induced hypercholesterolemia caused a marked increase in serum total cholesterol, triacylglycerols, LDL-C, VLDL-C, phospholipids, lipoprotein A, Apo B, endothelin-1 and homocysteine. On the other hand, a significant decrease in serum HDL–C and Apo A were observed in high cholesterol diet-induced hypercholesterolemia in rats. Treatment with flaxseed oil to high cholesterol dietinduced hypercholesterolemia rats lowered serum total cholesterol, triacylglycerols, LDL-C, VLDL-C, phospholipid, endothelin-1 and homocysteine concentration in addition to increasing HDL-C and Apo A. These results suggest that, flaxseed oil may be effective in controlling cholesterolemic status and improving dyslipidemia and has the potential in reducing cardiovascular complications due to hypercholesterolemia.