[Aim] To study whether Bursaphelenchus mucronatus secretes cellulase and whether this cellulase is related to its pathogenicity is not clear.[Method] We measured the cellulase activity of the protein extraction and secretion of two pathogenic species, B. mucronatus and B. xylophilus, and compared the differences in the isoforms of cellulose isozymes between the populations.[Result] Both the protein extraction and secretion of B. mucronatus contained cellulase. And there were some relativity between the cellulose activity and the pathogenicity of B. mucronatus, the stronger the pathogenicity, the stronger the cellulase activity.[Conclusion]Cellulase activity is an important reason for the difference in pathogenicity between different populations of B. mucronatus, which is of great significance for comprehensive understanding of the pathogenic mechanism of pine wilt disease.