Abstract: We dectected the activity of Bombyx mori carboxylesterase (BmCarE）in the midgetss by BIO-TEK SYNERGY between the silkworm strains HUABA which is susceptible to BmDNV-Z and BC8 which is resistant to the same virus. The expression differential of the BmCar was investigated after infecting 12,36 and 72 hours by Real-time fluorescence quantitative PCR. The results showed that : 1).The activity of BmCarE in the midgut of BC8 infecting virus after 12 hours was 3.28,2.26 and 3.02 times of that in the BC8 (water), HUABA (DNV)and HUABA (water) respectively (P＜0.01), and therer was no statistic difference among the three treatments BC8 (water), HUABA (DNV)and HUABA (water); 2).The quantity of BmCarE in the midgut of BC8 infecting virus after 12 hours was 17.714, 21.76 and 15.09 times of that in the BC8 (water), HUABA (DNV)and HUABA (water) respectively (P＜0.01), and therer was no statistic difference among the three treatments BC8 (water), HUABA (DNV)and HUABA (water); 3). The increase of BmcarE activity and the expression level related to the resistant gene (nsd/nsd) and the stimulation of BmDNV-Z; 4). The molecular base of the increase of BmcarE activity in the resistant strain BC8 was the change of carboxylesterase in the transcription level.