The larvae of Spodoptera litura were reared on an artificial diet, and the flight capability, and triacylglycerol (TG) level plus its fatty acid composition in 3-day-old sexually mature and non-fed adults were compared. In males, during 3 hr of tethered flight, the levels of abdominal TG and its fatty acid components did not change. But thereafter the TG and fatty acids, significantly unsaturated fatty acids in TG declined in their levels with the prolongation of flight, unsaturated fatty acids being exhausted preceding saturated fatty acid decline. When males were tested by tethered flight for 20 hr, some could fly for nearly the whole period, and were judged to be able to fly for approximately 24 hr, depending on the level of residual TG. Fatty aids in TG decreased in females similarly to males during tethered flight and some females with fully developed ovaries deposited eggs after 12 hr of flight similarly to non-flown individuals, which supports the long-distance flight capability even in sexually mature females. These results are discussed with regard to the overseas migration of this moth.