Nowadays, thermo-timber gets to the fore for its better resistance to wood-destroying fungi, insects and dimensional stability. The aim of the thesis was to determine the effect of thermal treatment on wood samples of winter oak (Quercus petraea, L.) The samples were thermally treated at 160 and 200 ° C for 3 and 9 hours. The samples were further subjected to the conical calorimeter method according to ISO 5660 (2002). where we obtained results from the field of fire characteristics: heat release rate, maximum rate of heat release, time to sample ignition, time to extinguish sample, total amount of heat released during test, and effective calorific value. We found out from the measurements that the thermal treatment had a positive effect on the monitored characteristics. The best results were obtained by thermally modified samples at 200 ° C and 9 hours, where the heat release rate reached the lowest value of 196.05 kW / m 2, which was 25.10% lower than the unmodified sample