Hyperlipidemia : is an elevation of lipids in the blood stream and these lipids include: fats, fatty acids, cholesterol, cholesterol esters, phospholipids, and triglycerides. Hyperlipidemia is associated with hepatic fat accumulation . Material and methods: Six groups (5rat/group) of female albino (Rattus albinus) were used. The 1st group used as control, in the 2nd group hyperlipidemia (25% fat & 2% cholesterol) was induced for 3 weeks only then sacrified , the 3rd group was hyperlipidemic rats for 3 weeks then left other 3 weeks without any additional treatment as a recovery period, the 4th group served as hyperlipidemic group for 3 weeks then treated with Avena sativa for another 3 weeks ( 200 g/Kg diet ), the 5th group was hyperlipidemic (25% fat & 2% cholesterol) for 6 weeks and the 6th group served as hyperlipidemic rats for 6 weeks, and at the same time given Avena sativa in diet (200 g/Kg diet). Results: The biochemical parameters showed highly significant increase in body weight, serum glucose, AST, ALT, GGT, LDH, urea, creatinine, total protein, albumin, total lipids, cholesterol, triglycerides and LDL-cholesterol, while there was highly significant decrease in HDL- cholesterol.Many histopathological and histochemical changes were detected in liver tissue of the hyperlipidemic rats. Meanwhile, the treatment with oat ameliorated the biochemical parameters, histological and histochemical results Conclusion: It is recommend to use oat in diets for hyperlipidemic patients or those people who have hyperlipidemic family history.