The main focus of this diploma thesis is the quality of the machined surface during planar milling of thermally modified wood. The introductory part deals with wood and its properties together with its use, which clarifies the reason for thermal treatment with saturated vapour and its detailed characteristics. The second chapter deals with the issue of face milling, which describes the principle of this extended wood chipping, its basic types and divisions, as well as the kinematics and machines and tools used. In the following third chapter, which is closely related to milling, the factors that have a significant effect on the quality of the treated surface are listed and characterized. With their suitable combination that is different for each wood and has not yet been explored in many, it is possible to achieve a relatively high-quality surface. A high-quality resultant surface in the face milling process means a surface of low corrugation and roughness. The fourth chapter is devoted to these two surface properties, in which the basic parameters of quality and methods of its measurement are mentioned. The last part of the work is a description of possible experimental work, which would provide significant knowledge about the behaviour of the surface quality of thermally treated birch wood samples, during planar milling.