Abstract: Using capsaicin as the lead compound, six series of 204 analogues, including 8 new compounds, were synthesized via N-acylation reactions using substituted benzylamines as precusors. The title compounds were characterized by ¹H NMR. Insecticidal activities of those compounds were determined by the leaf dish method. The results showed that most of the benzylamine derivatives had strong toxicities against the 3^rd Mythimna separata. The mortality rates of compounds A30 , D20 , D30 , D35 , E30 and F30 were 100% and compounds D19 , D21 , D22 , D23 , D31 and E31 were more than 90% against the 3^rd larvae at 10 µg/disc after 48 h. The preliminary study of structure-activity relationship indicated that the insecticidal activity of the mono-fluorine substitution on the benzene ring of benzylamine was better than that of the correspounding difluorine substituend compound. The 2-fluorobenzylamine derivatives showed better insecticidal activities than others. Additionally, 2-thiopheneformyl derivative exhibited significant insecticidal activity, which indicated that the acyl group was also an active fragment.