Abstract: The toxicity tests of the active principles of three Chinese drugs, namely Yang-chiao-ouApocynaceae, Strophanthus divaricatus(Lour.) Hook and Arn., Ya-tan-tze(Ku-shen-tze)Simarubaceae, Brucea joponica Merr. and Nao-yang-huaRhododendron hunnewellianum, with insects are described. It was found that Nao-yang-hua is must effective against the Hispa armigera, Ya-tan-tze is much less in its action, and Yang-chiao-ou is the least active one. On account of the widely growing and cheap price of Nao-yang-hua in China, it seems possible to be used as an insecticide.