MYC2 is a basic helix-loop-helix Leu zipper transcription factor (TF). Here, 22 putative soybean MYC-like TFs were identified bioinformatically. Of these TFs, seven MYC2-like genes without introns were isolated and characterized. All seven GmMYCs displayed transactivation activity in yeast cells. Six genes (excepting GmMYC3) were expressed in the roots, stems, leaves, flowers, and seed wall but not in the developing seeds and up-regulated after insect feeding. The GmMYC1 transgenic tobacco rejected common cutworm (CCW, Spodoptera litura Fabricius) more strongly and lost less leaf area than the control (2.94 +/- A 2.36 vs 7.84 +/- A 4.63 cm(2)). The average relative growth rate of CCW feeding on transgenic tobacco leaves was lower than on control tobacco leaves (136 +/- A 60 vs 271 +/- A 76 %). These results indicated that GmMYC could stimulate the defense mechanism against insects in plants.