This study was performed to investigate the effects of isoflavone consumption on plasma and liver lipid profiles and immune responses in Sprague-Dawley male rats. Experimental animals fed isoflavone at various doses for 4 weeks (0, 1095, 2190, 4380 isoflavone mg/kg diet). Exposure to isoflavone decreased the food consumption and final body weights of rats without decreasing the relative weights of organs, hemoglobin and hematocrit. And the plasma cholesterol and LDL-cholesterol, liver total lipid, cholesterol and triglyceride concentrations were significantly decreased by isoflavone intakes. The absolute and relative weights of thymus were significantly decreased in groups fed isoflavone than in control. Also splenocyte proliferations with Con A or PHA were decreased according to isoflavone consumption in rats, although there was not significant. These results demonstrate that isoflavone intakes significantly improve lipid profiles in plasma and liver. But the effects of isoflavone intakes on immune responses are needed further experiments.