By means of the reflux extracting and the systemic solvent separating method, the active parts were obtained from Euphorbia hylonoma Hand.-Mazz. Their bioactivity against armyworm, Leucania separata Walker, were determined by the conventional leaf disk method. The results indicated that petroleum ether and benzene extracts had strong antifeeding property and killing function on the 3rd larvae of armyworm, their antifeeding rate and mortality of 72 h were 100.0%, 100.0% and 80.0%, 83.3% respectively, which means that the substances having bioactivity were non-polar. Four kinds of component were obtained from its benzene extracts by column chromatography, except No.4 extract, the antifeeding rate of others in 72 h were all over 50% in 0.1% concentration.