Prostanoids play a pivotal role among the inflammatory mediators associated with I/R injury. The aim of this study was to determine the effects of oral supplementation of n-3 polyunsaturated fatty acids (PUFA)-rich oil on inflammatory reactions and microcirculatory disorders caused by a hepatic warm I/R in rats. The rats were orally supplemented with n-3 PUFA-rich oil, n-6 PUFA-rich oil, or the same volume of water for 7 days. The PUFA concentration in the blood and liver tissues were evaluated, and the effects on I/R injury of the liver were assessed. The n-3 PUFA supplementation elevated the n-3/n-6 ratio in the blood and liver tissues. After reperfusion, thromboxane B(2) in the blood and prostaglandin E(2) in the liver were significantly suppressed in the n-3 PUFA-treated rats. Hepatic microcirculation was well maintained from the early phase (30 min) of reperfusion, and the serum concentrations of TNF-alpha and IL-6 were significantly lower in this group. The transaminase blood levels were also suppressed in the n-3 PUFA-treated rats. Expression of COX-2 mRNA was increased in all groups at 2 h after reperfusion but there were no differences among three groups. In conclusion, preoperative n-3/n-6 ratio augmentation in the blood and in the liver can result in a successful alleviation of hepatic I/R injury.