Abstract: Monochamus alternatus is one of the most perilous wood-boring insect pests in pine plantations in southern China, and the enzyme cellulase plays the major function to digest the ingested woody tissue in its gut.The cellulase extracted from larvae of M.alternatus was tested to determine its constitution and kinetic properties in this paper.The results revealed that the longicorn borers had integrated cellulolytic enzyme complex: endo-β-1,4-glucanase （Cx-ase）,exo-β-1,4-glucanase （C1-ase） and β-1,4-glucosidase in their gut, among which the activity of C1-ase was the strongest, and β-1,4-glucosidase the weakest.For C1-ase, Cx-ase and （β-1,4-glucosidase）,the optimum temperature range was between 35～55 ℃, 45～55 ℃ and 40～50 ℃ respectively, while their optimum pH at 5.0,5.6 and 5.0. Besides, Cx-ase had the stronger stability to heat,which still had strong activity after being heated at 65 ℃ for 2 h. After comparison of the kinetic parameters among the cellulases of M. alternatus,it was found that C1-ase had greater Vmax and Km,which was 1.083 8 and 0.763 2 respectively,however,β-1,4-glucosidase had greater relatively muzzle velocity.