The diploma thesis deals with the application of spectral methods for the evaluation of thermal degradation of wood after loading by a heat source. The theoretical part of the work is a literary review of the issue of the influence of heat on changes in chemical and physical properties of wood, as well as the principles and use of selected spectral methods in the evaluation of thermal degradation of wood. The content of the practical part is an experiment performed on samples of spruce wood, heat treated at different temperatures. The colour changes of the surface and changes in the structure of lignin as one of the main wood components were evaluated by spectrophotometric and FTIR methods. The results of the work can be used in the field of evaluation and increase of fire protection and safety in the use of wood as a construction material.