The diploma thesis deals with the issue of thermal stability of structural materials. The aim of the work is to assess the stability of wood based on using thermal analysis methods. Wood is often used as a construction material for construction because it has good physical and mechanical properties. It is mainly used for the construction of historical, folk buildings or wooden buildings, which are widely spread in some parts of the world. We investigate specimens of wood by thermal analysis, thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), namely specimens of spruce and oak. The influence of the heating rate on the sample was monitored during the thermal analysis. By thermal analysis, it was found that spruce wood decomposes more at lower heating rates because, at higher heating rates, a charcoal layer is formed on the surface of the wood to prevent more massive thermal decomposition. For oak wood samples, the heating rate has not a significant influence because the mass residue at different heating temperatures was approximately the same. When comparing spruce and oak wood, the measurement showed that with oak wood the heating rate is not so prominent, but with spruce wood, the heating rate of the samples has a great impact on the mass residue. The thermal stability of spruce wood is lower because it shows higher temperature values of maximum mass loss than oak wood.