The thesis deals with thermally modified beech wood, which was modified in atmospheric conditions of heated temperature 160°C and 200°C. for 1 , 3 and 5 hours, weathering conditions. Samples were exposed from September 2017 to March 2018 (six months). Color change, roughness and occurrence of cracks was monitored. The color deviation ΔE* was measured by color system CIE L*a*b*. During the aging, there was mainly darkening of wood (decrease in wood brightness - ΔL *) and the wood surface became greyish. The concentration of impurities in the air during the heating season has significantly influenced the nature of the color changes of the control samples during the first two months..Roughness was measSured on basic parameters: arithmetial mean roughness value, arithmetical mean quadratic roughness value maximum roughness depth (peak to valey). The influence of timelenght on roughness was statistically significant The most significant production of cracks was monitored with termowood modified by 200°C within 3 and 5 hours. During the exposition the number of cracks has increased and the largeness of cracks. After 90 days was found on the surface of termowood plucking of fibres. After 180 days the occurence of plucking of fibres was more obvious. On the pattern of color changes of termowood was probably the most influenced by concentration of impurities in the atmosphere during heating season.