For investigating the possible importance of a trypsin-like protease produced by Rhizoctonia cerealis Vander Hoeven in infection process of the pathogen, the changes of protein content in extracted cell wall and hydroxyproline content released from it after treatment with the protease were tested. The result indicated that the ability of protease to degrade structural proteins in the wheat cell wall. The impact of this protease on wheat tissue observed by transmission electron microscopy showed that it participated in degradation of the host membrane protein during infection. The protease activity detected in both control and infected plant material throughout infection indicated that R. cerealis produced trypsin-like protease and other protease in pathogenesis.