In this study, the insecticidal activity of alcohol extraction of Metaplexis japonica, Taraxacum mongolicum and Picris davarlca were researched. We determined the larval mortality percentage of 3th instar larvae of Tenebrio molitor exposed to alcoholic extract of 3 species using the method of the micro-drop and the feeding method. The re-sult showed that alcohol extraction of three kinds of lactic plants were toxic to 3th instar larvae of Tenebrio molitor,toxicity from strong to weak were Metaplexis japonica, Taraxacum mongolicum and Picris davarlca. The Larval LD₅₀ of 3th instar larvae of Tenebrio molitor exposed for 24 hours to alcoholic extract of Metaplexis japonica, Taraxacummongolicum and Picris davarlca using the method of the micro-drop method were 618.07, 865.84 and 1 184.17μg/larva.