Abstract: In order to clarify the function of Cathepsin B gene (NbCathB) in Nicotiana tabacum, the sequence of NbCathB was analyzed. The NbCathB ORF (Open Read Frame) was 951 bp in length and encoded 316 amino acids with the predicted molecular weight of 35.2 kD and isoelectric point of 6.14. The analysis of NbCathB gene structure revealed that there were 8 exons in NbCathB and all of them conformed to GT-AG rule. NbCathB shares 61% identity in encoded amino acid sequence with Arabidopsis thaliana Cathepsin B (AtCathB). SMART software analysis indicated that, NbCathB and AtCathB had similar structural domain. The expression of NbCathB in tobacco leaves which treated by the deposit and bacterial liquid of MP agents were higher than those treated by the supernatant of MP agents (Bacillus magaterium). The expression of NbCathB in tobacco leaves treated by water was the lowest. The results indicated that the function of NbCathB might be similar with that of AtCathB.