Tricholoma matsutake, an ectomycorrhizal fungus, is the most expensive mushroom at the region of northeastern Asia. Since the mushroom is edible, it is very serious to have a parasitic fungus on the surface of fruit-body. We discovered a necrotrophic mycoparasite of T. matsutake. We tried to illustrate the feature of mycoparasite on T. matsutake in detail, and it was identified as Syzygites megalocarpus.