Abstract: The toxicity and selection of insecticides to Coccinella septempunctata（L.）and Brevicoryne brassicae（L.）are studied.The results show that the selective toxicity of imidacloprid is the highest among 15 insecticides tested,and the selective toxicity ratio （STR,ladybird LD₅₀/aphid LD₅₀）reaches 174.29.Among 5 organophosphorus insecticides,malathion shows the highest selec tivity,and the second is dichlorvos,their STRs are 35.73 and 25.32,respectively.Cyfluthrin and cypermethrin among 7 pyrethroid insecticides possess the highest selective toxicity for the aphid to the ladybird, the STRs are 55.16 and 30.00,respectively.Therefore the high selective insecticides, such as imidacloprid,cyfluthrin and malathion,not only possess the high toxicity to aphid,but also are safe for the natural enemy,ladybird,and are relatively ideal insecticides for controlling aphids in the field.