Abstract: The effect of dietary incorporation of soybean, a high isoflavone-containing legume, on serum marker enzymes, lipid profile and relative organ weights of wistar rats was studied. Male wistar rats weighing between 100-200g were divided into four groups. Group 1 was fed normal rat chow while groups 2, 3 and 4 had normal rat chow supplemented with 10, 25 and 50% soybean, respectively, for fourteen days. At the end of the feeding experiment, the rats were euthanised by chloroform anesthesia and the serum obtained were used for the biochemical assays. In all cases, the rats had free access to feed and water. The results of the study showed that high intake of soybean (25% and 50%) in the diet significantly (P<0.05) reduced the level of the serum enzymes; glutamate – oxaloacetate and glutamate pyruvate transaminases, alkaline and acid phosphatases and serum glucose. Supplementation of soybean at these levels also increased serum vitamin C. Insignificant decreases were found in the liver, kidney and testis relative weights, serum low density lipoprotein and lipid peroxidation products (Malondialdehyde) levels. Soybean incorporation at the 50% level significantly reduced total serum cholesterol. These findings support the reports of the beneficial and health promoting effects of soybean.