The inhibition of cell proliferation,cell morphological change and mitochondrial membrane potential change of ethanol extracts of 20 Thailand plants on Spodoptera litura (Sl-1) cell were investigated by MTT test,inverted phase contrast microscope and flow cytometry,respectively.The results showed that the Sl1 cell proliferation inhibition effect of 5 ethanol extracts including Thailand plants (Zingiber officinale Roscoe, Alpinia galangl (L.) Willd.,Azadirachta indica A.Juss var.siamensis Valeton,Curcuma longa Dennst and Citrus hystrix DC) was better than that of the control rotenone,and the inhibition was dosedependent. After 24 h of the treatment,cells showed obvious morphological changes,including adhesion capacity reduction,vacuole and debris appearance.After 48 h of the treatment,more and more vacuoles and debris were present obviously in the media.Moreover,these five ethanol extracts could induce cell mitochondrial membrane potential change,among which A. indica A. Juss-var. siamensis Valeton and C. hystrix DC were more effective.In conclusion,Z. officinale Roscoe,A. galangl (L.) Willd.,A. indica A. Juss var. siamensis Valeton,C. longa Dennst and C. hystrix DC possessed cytotoxicity on Sl-1 cells and deserved further researches.