There is an increasing interest in the potential of isoflavone in reducing the risk of cardiovascular disease and cancer, however, although several effects of isoflavone as a component of soy protein are well established, the hypolipidemic and antioxidant effects of purified isoflavone are still controversial. This study was to investigate the effects of isoflavone on serum lipid profiles and antioxidant status in rats. 7-week old male Sprague Dawley rats were fed one of the following diets for 8 weeks: basal diet (B), basal+0.3% isoflavone (BI), basal+0.5% cholesterol (BC), or basal+0.3% isoflavone +0.5% cholesterol (BIC). Two-way ANOVA was used to test the effects of dietary isoflavone and cholesterol supplementation and their interaction on variables. Serum lipid profiles and total antioxidant status (TAS) were examined spectrophotometrically. Degree of serum lipid peroxidation was measured by malondialdehyde (MDA) assay. The activities of serum antioxidant enzymes (GSH-Px, total-SOD) was determined. Levels of serum total cholesterol, VLDL+LDL-cholesterol and Atherogenic index were significantly lower in BI than those levels in group B (p=0.0002, p<0.0001, and p=0.0042, respectively).Serum total antioxidant status (TAS) levels were significantly higher, in both isoflavone supplemented groups (BI, BIC) compared to those levels in each control group (B, BC) (p<0.0001). Activity of total-SOD was significantly higher in BI compared to the activities in group B (p=0.0317). There was no interaction between isoflavone and cholesterol supplementation. In conclusion, isoflavone supplementation showed positive effects on the serum lipid profiles and total antioxidant activities in both conditions, either when fed a diet with or without cholesterol. These effects of isoflavone were independent of cholesterol supplementation.