【Background】After the widespread planting of Bt cotton in China, the target pests cotton bollworm, Helicoverpa armigera and the pink bollworm H.zea were no longer major pests. However, two other herbivores, Spodoptera exiguaand S.litura remained important. The Cry2Ab protein, expressed in BollgardⅡ cotton seems to have higher effects against these two pests. In this paper, the effect of Cry2Ab protein on these lepidopteran pests was investigated. 【Method】The effects of different Cry2Ab protein concentrations （1.25, 2.5, 5.0, 10.0 and 20.0 μg·g-1） mixed into artificial diet on the survival rate and growth rate inhibition in S.exigua and S.litura were described under laboratory conditions. 【Result】With the increase of Cry2Ab protein concentration, first-instar and neonate larvae of S.exiguadisplayed a lower survival rate, but second and third-instar arvae of either species showed no significant differences compared with the control. However, body mass of these two insects was obviously negatively affected by feeding on Cry2Ab protein containing diets. 【Conclusion and significance】High concentrations of Cry2Ab protein (10.0 and 20.0 μg·g-1) had stronger effects against neonates and first-instar S.exigua larvae but had little effect against S.litura.