Thesis investigates possibility for chemical modification of beech, spruce sapwood and pine with an agent, the main component of which is imidazol derivative - dimethyloldihydroxyethyleneurea (DMDHEU). Two different concentrations of agent (5 and 20 %) at two reaction temperatures (150 and 170°C) were used for modification. Reaction process and degree of modification were evaluated by weight percent gain (WPG). Differences in equilibrium moisture contents between modified and control samples and antishrinking efficency (ASE) were determined. Influence of modification process on leachability (SIST EN 84) of the modified samples was also investigated. Optimal results were achieved with 20 % solution and 170 °C. By the stated parameters the highest rate of agent crosslinking was observed. By this modification method we achieved better dimension stability and lower equilibrium moisture contents of modified samples compared to control samples.