In accordance to the development and guidelines of environment protection, protection procedures which are less harmful to humans and environment but nevertheless efficiently protecting wood against biotic factors of decay were developed. For the purpose of wood modification, nowadays the wood modification water soluble resin - dimethyilol-dihydroxyethyleneurea (DMDHEU) -is being developed, and has already been used for many years in the textile industry for modification of cellulose in cotton fabric. It was researched whether the wood modified with this agent, known under the brand name Meldur, was resistant to wood decay caused by fungi. In accordance to the amended standard SIST EN 113 (1995), the modified samples were exposed to 5 fungi species. The spruce and beech wood samples were exposed to the influence of the following fungi: Gloeophyllum trabeum, Antrodia vaillantii, Coniophora puteana, Trametes versicolor and Hypoxylon fragiforme. The results showed that the modified spruce wood samples were very efficiently protected against the decay caused by Gloeophyllum trabeum and Antrodia vaillantii fungi. Similarly, the modification with 10 % concentration of Meldur at 2 modification temperatures protected the spruce wood samples against Trametes versicolor as it was expected. The mass loss of beech wood samples exposed to Antrodia vaillantii and Trametes versicolor was higher compared to test samples. Only the modification of the beech wood samples with 10 % concentration of Meldur at 150 °C achieved the expected protection against Hypoxylon fragiforme. In general, the modification of spruce and beech wood with Meldur sufficiently protects wood against the decay caused by brown rot fungi while it is less effective against white rot fungi.