In the territory of the Transcarpathian region of Ukraine we first identify and characterize Armillaria tabescens (Scop.: Fr) Emel species of basidiomycete genus which known as causal agents of root rot on a wide range of woody plants through over the world. The fruiting bodies were collected in four different localities of the lowland oak-dominated forests managed by sylviculture. Significantly, basidiocarps were found on dead wood remnants and almost never on living trees. We described morphological, microscopic and molecular characteristic of collected specimens and determined phylogenetic relationships between A. tabescens from Ukraine and from other parts of the world by analyzing the genetic variation in the IGS-1 of rDNA.