Abstract: To investigate the effects of insects with different mouthparts feeding on tobacco leaves on the signal molecules and secondary metabolites in tobacco, Myzus persicae (with a piercing-sucking mouthpart) and Spodoptera litura (with a chewing mouthpart) were fed on tobacco leaves. The contents of alkaloids and sucrose ester (SE) in tobacco leaves were determined 3, 6, 10, and 15 days after feeding and the contents of nitric oxide (NO) and jasmine acid (JA) in leaves and roots were determined 3, 6, 9, and 12 hours after feeding. The results showed that:After M. persicae and S. litura feeding, 1) the contents of nicotine, nornicotine and total alkaloids increased first, peaked on the 6th day and then decreased. Comparing with the control, the contents of nicotine, nornicotine and total alkaloids in tobacco leaves raised by 89.80%, 27.92% and 82.20% after M. persicae feeding, and by 84.06%, 34.31% and 79.15% after S. litura feeding, respectively; 2) the content of SE in tobacco leaves reached its highest on the 10th day and increased by 60.14% and 65.90% comparing with the control, respectively; 3) the contents of NO in leaves and roots increased first, peaked at the 9th hour and then decreased. The contents of JA in leaves and roots increased significantly. In leaves, JA increased first and then decreased, while JA continued to raise in roots.