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Wheat (<i>Triticum aestivum L</i>.) is an important staple crop. <i>Rhizoctonia cerealis</i> is the causal agent of diseases that are devastating to cereal crops, including wheat. Xylanases play an important role in pathogenic infection, but little is known about xylanases in <i>R. cerealis</i>. Herein, we identified nine xylanase-encoding genes from the <i>R. cerealis</i> genome, named <i>RcXYN1&#8722;RcXYN9</i>, examined their expression patterns, and investigated the pathogenicity role of RcXYN1. RcXYN1&#8722;RcXYN9 proteins contain two conserved glutamate residues within the active motif in the glycoside hydrolase 10 (GH10) domain. Of them, RcXYN1&#8722;RcXYN4 are predicted to be secreted proteins. <i>RcXYN1&#8722;RcXYN9</i> displayed different expression patterns during the infection process of wheat, and <i>RcXYN1</i>, <i>RcXYN2</i>, <i>RcXYN5</i>, and <i>RcXYN9</i> were expressed highly across all the tested inoculation points. Functional dissection indicated that the RcXYN1 protein was able to induce necrosis/cell-death and H₂O₂ generation when infiltrated into wheat and <i>Nicotiana benthamiana</i> leaves. Furthermore, application of RcXYN1 protein followed by <i>R. cerealis</i> led to significantly higher levels of the disease in wheat leaves than application of the fungus alone. These results demonstrate that RcXYN1 acts as a pathogenicity factor during <i>R. cerealis</i> infection in wheat. This is the first investigation of xylanase genes in <i>R. cerealis</i>, providing novel insights into the pathogenesis mechanisms of <i>R. cerealis</i>.