Abstract: A transgenic Bt maize hybrid expressing Bacillus thuringiensis (Bt) toxin, Cry1Ab protein, and its negative isoline hybrid were evaluated for against the Asian corn borer, Ostrinia furnacalis (Guenée), in field trials and laboratory bioassays. The Bt hybrid, NX4777, was developed by Novartis Seeds, using event Bt11, which expresses Bt toxin in green tissue as well as reproductive tissues including the tassel, silk, and kernel. Bt hybrid was compared with the negative isoline control, NX4906. Maize plants were artificially infested with neonate larvae of the Asian corn borer at the mid-whorl, pre-tasselling, and silking stages. Hybrid resistances were based on leaf feeding ratings, larval controls, as well as stalk and ear damages. Bt hybrid sustained significantly less leaf feeding damage (rating 1) than its negative isoline control (rating 7). On average, there were only 0.04~0.20 larvae survived per plant, 0.11~0.15 tunnels per stalk with 0.13~0.41 cm tunnel length per plant, respectively, and none of plants were stems broken or ears damaged on Bt hybrid under different infestations. In contrast, there were 6.19~12.41 larvae survived per plant, 4.48~7.05 tunnels per stalk with 12.41~24.09 cm tunnel length per plant, respectively, and 73.6%~95.5% plants were stems broken and ear damage ratings was 5.9 on the negative isoline control. Laboratory bioassays indicated that there were only 0~1% of larva survived when neonates fed on fresh whorl leaves, young tassel, and fresh silk of Bt hybrid, compared with more than 88.7% of larvae survived on the negative isoline control. These results demonstrate that transgenic Bt maize can provide season-long control of the Asian corn borer.