Abstract: The effects of the crude extracts from Periploca sepium Bunge on the bioactivity of imported cabbage worm were studied. The results show that the effect of ethanol extract on the bioactivity of imported cabbage worm is higher than that from chloroform and petroleum ether extracts. The main insecticidal actions of the ethanol extract include the strong antifeedant activity and the growth inhibition and certain action of stomach poisoning to the larvae of imported cabbage worm. Antifeeding rate with dilution of 100 times is 94.9%, 87.8% and 92.7% against the 3rd, 4th and 5th instar larvae respectively in no choice test, and the rates of growth inhibition on the 4th instar larvae are 96.6% and 82.5% in 24h and 72h after treatment. The pupating and weight of pupaes are much lower than that of control. The crude extract has obvious detertory effect against the oviposition of imported cabbage worm. Oviposition deterrent rate is over 89.5%in 2～4d after treatment when the seedlings are sprayed by ethanol extract with dilution of 50～100 times.