The root barks of Periploca sepium Bunge were hot-extracted with 95% ethanol, and leaf immersion method and topical application were used to test the bioactivity of the extracts against Plutella xylostella L. The results indicated that antifeeding rate was 87.3% and 96.3% against 3rd and 4th instar larvae of P. xylostella after 24 h of treatment with 100 times dilution of the ethanol extracts in no-choice test respectively. The corrected mortality of the larvae within 72 h reached 80% when the 2nd instar larvae of P. xylostella were fed by the leaf discs treated with 100 times dilution of the extracts. The growth inhibition rate of 100 times dilution of the extractwas 100% to 3rd instar larvae. It is clear that the ethanol extracts has strong antifeeding property, stomach poison and growth inhibition to larvae of P. xylostella. In addition, the ethanol extracts of P. sepium possesses certain contact poison and systemic toxicity on the insect. The experimental results also showed that the crude extracts had obvious deterrent effect against the oviposition of P. xylostella. However, the extracts showed no killing effect on the eggs of P. xylostella.