Wood is an important natural renewable material and its possibilities for use are great. You can improve the properties of wooden material by thermal modification. In the diploma thesis we monitored changes in the chemical composition of spruce wood, density and colours at 20, 160, 180, 200 and 220 °C. We found out that the amounts of lignin, cellulose and extractives increase with increasing load temperature. The polysaccharide part degraded significantly, with the content hemicelluloses and holocelluloses decreased. We also found out that it decreases due to thermal modification wood density and color change depending on the applied temperature. In addition, a literature search focused on lignocellulosic materials was carried out, thermal wood and thermal modification of Norway spruce.