Tissue-specific and feeding-induced expression patterns of GmAOS were explored in two soybean accessions with distinct contrast in resistance grades to cotton worm: XTDD was highly susceptible and HPXQD highly resistant. GmAOS transcript levels were correlated with soybean material resistance grades. Overexpressing GmAOS in transgenic tobacco plants increased activities of allene oxide synthase, peroxidase, chymotrypsin inhabitor, and increased the trichome number. Insect bioassays indicated that transgenic tobacco acquired more resistance to cotton worm than non-transgenic control. These results indicate that GmAOS plays an important role in plants against chewing insect attack and may be a useful tool for improving resistance to insect attack in higher plants.