People who take onion (Allium sativum) supplements hope to improve their well-being and to reduce the risk of various diseases. Numerous myths about its medicinal properties have existed for centuries in various cultures. According to some investigators the lower incidence of widespread disease in southern countries may partly be due to consumption of large quantities of onion. The objective of this study was to determination of onion (Allium cepa. linn) extract on the serum concentration of cholesterol, triglycerides, LDL and HDL. In this experiment, 162 mature male rats (250 gm on the average) were acquired from Razi Serum–producing Institute of Karaj and transferred to keeping place and then divided into the 9 identical groups. In the present study, lipids of serum were significantly decreased consequent consumption of onion extract. In conclusion can be state that onion and zinc sulfate have the most important hypolipidemic effects that combined use of these elements showed best effect than alone use.