Domain I of the activated Crystal protein from Bacillus thuringiensis has a seven α-helix bundle structure, which is responsible for membrane channel formation in its insecticidal mechanism. Cry1Ie is toxic to Asian corn borer, Ostrinia furnacalis(Guenée), and plays important roles in insect biological control. The domain I from Cry1Ie has been expressed and purifi ed in its normal conformation, as embedded in the full length homologous toxin structure. The membrane insertion ability of this single domain was compared with the full length homologous toxin using a monolayer insertion experiment. The results indicated that the Cry1Ie-domain I had the ability to insert into the lipid monolayer, and this ability is greater than that of the IE648 toxin. However, the state of insertion is not stable and remains for only a short period of time. The Cry1Ie-domain I plays no role in receptor binding as it had a nonspecifi c binding with the brush border membrane vesicles of the Asian corn borer. Domain I of the activated Crystal protein from Bacillus thuringiensis has a seven alpha-helix bundle structure, which is responsible for membrane channel formation in its insecticidal mechanism. Cry1I is toxic to Asian corn borer, Ostrinia furnacalis (Guenée), and plays important roles in insect biological control. The domain I from Cry1Ie has been expressed and purifi ed in its normal conformation, as embedded in the full length homologous toxin structure. The membrane insertion ability of this single domain was compared with the full length homologous toxin using a monolayer insertion experiment. The results indicated that the Cry1Ie-domain I had the ability to insert into the lipid monolayer, and this ability is greater than that of the of IE648 toxin. However, the state of insertion is not stable and remains for only a short period of time. The Cry1Ie-domain I plays no role in receptor binding as it had a nonspecific c binding with the brush border membrane vesicles of the Asian corn bor er.