Beech-wood has favourable mechanical properties, which make the timber of this species suitable for construction purposes. At the same time the wood is not resistant to biological deterioration and has unfavourable dimensional stability. These properties reduce its suitability to be used for structural purposes, especially in aggressive climatic conditions favourable for inoculation with fungi or insects. Thermal modification helps to improve durability and dimensional stability of wood. At the same time it might negatively affect other (including mechanical) properties. Experimental and numerical analysis of a compression test carried out on samples of as-received and thermally-treated beech (Fagus sylvatica L.) wood is presented. Samples were exposed to static compressive loads parallel and transverse to the grain. Afterwards, the test was modelled using the finite element method. It was confirmed that, after thermal modification, the wood’s density decreased and the stiffness in both tested directions increased. After the thermal treatment, the strength of beech wood increased in the direction parallel to the grain and decreased in the direction transverse to the grain. Based on the comparison of experimental and numerical results, it is possible to use the hyperelastic constitutive law to reasonably model the force and displacement obtained in the compression test samples. The results of this study will help to use thermally modified beech wood for construction purposes.