This study was performed to investigate the effects of genistein, a kind of soy isoflavones, on fatty liver and lipid metabolism in rats fed high fat diet. Twenty four male Sprague-Dawley rats were divided into four groups by dietary fat and genistein contents then raised for six weeks. The rats(n=6/group) were fed normal fat diet(NOR), high fat diet (HF), high fat with 0.1% genistein(HF+0.1%G) or high fat with 0.2% genistein(HF+0.2%G). Hepatic total lipid, triglyceride, total cholesterol and Serum GPT, as a marker for fatty liver, were significantly increased by high fat diet. Also, serum total lipid, triglyceride, total cholesterol, glucose and insulin concentration, hepatic lipogenic enzyme (fatty acid synthase and malic enzyme) activities were significantly increased by high fat diet. However, hepatic total lipid, triglyceride, total cholesterol and Serum GPT were significantly decreased by genistein intake. Also, genistein supplementation decreased serum total lipid, triglyceride, glucose and insulin concentration, hepatic lipogenic enzyme (fatty acid synthase and malic enzyme) activities. There were no differences by genistein level except for serum insulin. These results suggest that fatty liver induced by high fat diet was caused by increased serum lipid profiles and hepatic lipogenesis, whereas, genistein may be useful in inhibiting of fatty liver by reducing serum lipid profiles and hepatic lipogenesis.