The article is devoted to the study of the component composition of mycologically destroyed wood. As a result of wood mycolysis under the action of wood-destroying fungi enzymes, so-called «rot» is formed with a chemical composition different from healthy wood. It is noted that the «brown rot» of wood is enriched with lignin components of wood and «white rot» with carbohydrate components of wood. The results of analyses of ligno-carbohydrate complexes of spruce wood «brown rot», birch wood «white rot» and a group study of low-molecular compounds isolated by extraction methods with various solvents are presented. It is noted that the content of lignin in the sample of «brown rot» wood is four times higher than in the sample of «white rot». It is shown that birch wood with «white rot» is significantly enriched with cellulose. The chemical nature of some groups of extractive substances has been revealed. In the extracts of mycologically destroyed wood, substances of phenolic, alcoholic and quinone nature were found. The presence of derivatives of aromatic and aliphatic carbonyl and carboxyl compounds is noted. Among the products of mycolysis, carbohydrates, flavanoids and terpenoids have been identified. Based on the analysis, an assumption is made that mycologically destroyed wood contains a wide range of phenolic and carbohydrate compounds contained both in the original wood and in the spores and hyphae of wood-destroying fungi themselves. The idea is substantiated that the study of extractive substances of mycologically destroyed wood makes it possible to predict possible directions of the prospective use of this raw material for obtaining target products. This article is the fourth in the cycle «Wood mycolysis, its products and their use», the previous ones were published in the journal «Forestry Bulletin», 2020, v. 24, no. 2, 6; v. 25, no. 1.