Phospholipids of the cell membrane have been studied from the viewpoint of how overwintering insects inhabiting temperate zones adapt to low temperature. The transition of cell membrane phospholipids from a liquid crystalline phase to a gel phase is a crucial cause of cold or freezing injuries. We determined the qualitative and quantitative changes of phospholipids in the last instar larvae of the rice stem borer in summer and winter. We found that the total amount of their phospholipids did not change significantly between summer and winter and that the sum of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) comprised about 85% of their total phospholipids. In summer, the ratio of their PE to PC was almost one, while from autumn to mid-winter it increased and reached three in February. The fatty acid compositions of PC hardly changed, and the percentage of unsaturated fatty acids did not exceed 50%. In contrast, the percentage of unsaturated fatty acids of PE in overwintering larvae increased up to 80% as ambient temperatures fell and oleic acid mainly contributed to the high percentage of unsaturation. In the present study, the relationship between the quantitative and qualitative changes of phospholipids and adaptation of the rice stem borer to cold winter climate are discussed.