This research cleared the function of four enzymes (Phenylalanine ammonia-Lyase, Polyphenol Oxidase, peroxidase and catalase) in wheat resistance to Sitobion azvenae (Fabricius) . Five wheat, two high-resistant cultivars/selections (KOK1679 and My295), one middle-resistance cultivars (Li), and two susceptible cultivars (Beijing837 and Beijing411) were been researched. The Phenylalanine ammonia-Lyase, Polyphenol Oxidase and peroxidase activity of aphid-resistant wheat were higher than aphid-susceptible wheat...