The experiments were conducted in laboratory to explore the effects of transgenic. The activtiy changes of detoxification enzymes and midgut protease after feeding on the pollen of transgenic Bt (Bt-cry1Ah) maize in the ladybird beetle Propylaea japonica (Thunberg) was examined. The activities of the α-naphthylacetate esterase， acetylcholinesterase, glutathione-S-transferase, total protease, alkaline trysin-like proteinase and chymotrypsin-like proteinase in beetles reared Bt and non-Bt maize pollen were compared by feeding the on transgenic Bt-cry1Ah maize pollen combinded with colorimetric method. The results indicated that there were no differences in the activities of acetylcholinesterase, glutathione-S-transferase, total protease and active alkaline trysin-like proteinase in P.japonica in any examined larval instars of larvae and adults fed on transgenic Bt maize pollen vs. those fed on non -Bt pollen (the control). The activity levels of α-naphthylacetate esterase in 4th instar larvae and pupae, and the weak alkaline trysin-like proteinase and chymotrypsin-like proteinase in P.japonica at pupae fed on transgenic Bt maize pollen were significantly lower in beetles feeding on transgenic pollen than that in the control. Therefore, the interation of the detoxification enzymes and midgut proteases and Cry1Ah protein may cause some of the enzymes activities. The potential impact of transgenic Bt-cry1Ah maize pollen on P.japonica need to futher study.