No. 3 diflubenzuron is one type of benzoyl N-Phenylurea compound, a type of insect chitin synthesis inhibitor, and has a unique disinsection mechanism. It can depress the chitinous formation on the insect epidermis, and make it die in the process of ecdysis or metamorphism. It has particularly effective impact on lepidopterous larvae, and it can control many kinds of pests?such as armyworm, cabbage worm, cotton bollworm?Clanis bilineata, Pine caterpillar, Hyphantria cunea? mosquito screwworm etc. No. 3 diflubenzuron hardly has effect on imagoes, and has low virulence on higher animals; the medium lethal dose of white rats is 15,000 mg/kg on w/w basis. It has high virulence on target insects, but low virulence on non-target insects. This chemical has no specific smell, does not pollute the environment, and is safe for humans and animals. Thus, it is a new diflubenzuron with high-effect and low-virulence, and could replace some organochlorine insecticides such as DDT, Hexachlorocyclohexane and others. Mythimna separata Walker is one of the main pests of crops in Jilin Province. The infested area per year is usually 5 – 10 million mu [666.7m2 ] in the whole province; and it will reach above 10 million mu in years of mass-outbreak. It leads to severe reduction of yield or even no yield if the M. separata are not controlled in time. In order to replace the organo-chlorine pesticides with their highly toxic residue?we have been doing experimental investigations and research on the chitin synthesis inhibitors - No. 1 diflubenzuron and No. 2 diflubenzuron - since 1977. In addition, we have done systemic research on No. 3 diflubenzuron supported by leaders in the Science Committee of our province since 1979. Our results are from indoor control experiments of No. 3 diflubenzuron colloidal suspension M. separata, which was synthesized and provided by the Tonghua Chemical Engineering Institute, and field-plot experiments and demonstration extension experiments within Jilin province. In this paper, the partial results of our research are summarized as follows.Originating text in Chinese.Citation: Liang, Shulian, Sun, Yajie, Chen, Ruilu. (1985). Experimental Report on the Effectiveness of the Insecticide Chloromethiuron 3. Journal of Jilin Agricultural Sciences, 35(2), 36-44