The effect of isoprothiolane(di-isopropyl-1,3-dithiolan-2-ylidenemalonate) aganist fat necrosis in Hanwoo(Korean Cattle) sire was evaluated. The 10 heads of Hanwoo sire suffering from fat necrosis were given 50mg/kg body weight of isoprothiolane(0.2g/kg of Fujix, Japan) orally once a day for 8weeks. In 30% of these, the size of thenecrotic fat masses had decreased significantly 7 months after the adminstration. Isoprothiolane did not affect on live body weight and semen characteristics. However the sire affected with fat necrosis had higher MCHC(Mean corpuscular hemoglobin concentration) than normal sire inhematologic values 10 weeks after administration. Number of RBC(red blood cell) and PCV(packed cell volume) 10 weeks after administration had been increased than those before administration(p0.05). The serum concentrations of creatinine, triglyceride, and total cholesterol 10 weeks after administration were higher than those before administration while the concentration of glucose was vice versa. the isoprothiolane may reduce the oxidation of glucose, increase the glucose transfer to lipids, and increase blood supply to necrotic masses. These results indicate that isoprothiolane may be useful as the therapeutic agent against fat necrosis.