In this study we investigated the effects of dietary fat sources and onion on serum lipid levels in rats. One hundred twenty female Wistar rats two weeks old were randomly divided into five groups of 24 animals assigned to one of the ive modalities : Control group was fed only basal diet containing 6.3% of corn oil, T and L group were administered 6.3% beef tallow and lard substituted for corn oil in basal diet, LOv and LOx group were given same amount of lard as L group together with 4.2ml of onion juice/kg body weight, and 8.2ml of onion juice/kg body weight respectively. Six randomly selected rats from each group were evaluated for hematologic and serum biochemical parameters weekly. Over 4 week experiments it was found that the triglyceride and cholesterol levels were significantly elevated in T and L group compared with the control group. Triglyceride contents were significantly increased in L group compared with T group. But there was no difference in cholesterol levels between L and T group. LOv diet did not decrease significantly the triglyceride and cholesterol levels, but LOx group significantly did compared with L diet. LOx group had nearly normal values of bilirubin, creatinine, uric acid level and hemoglobin contents cut slightly increased levels in the glutamic oxaloacetic transaminase and alkaline phosphatase activities.