Abstract: Cathepsin gene Bmcath1 of Bursaphelenchus mucronatus is differentially expressed between B. xylophilus and B. mucronatus. In order to understand its biological function, bioinformational analysis was conducted using software BioEdit, SignalP 4.1, BLASTP and MEGA 4. 0. The result showed that the full-length cDNA of Bmcath1 was 1 294 bp long, which included an ORF of 1 158 bp. The deduced amino sequence of CATH1 contained 386 amino acids with molecular mass of 42.38 ku and pI of 8.52. Protein CATH1 contained a Peptidase-C1A conserved domain. The amino sequences of cathepsins varied between different species. With the method of real-time PCR, gene expression profiling showed that Bmcath1 expressed much more in B. mucronatus separated from Pinus thunbergii seedlings comparing with expression level of Bmcath1 in monoxenic culture nematodes. The result suggested that function of Bmcath1 may be related to infection process of B. mucronatus.