Nowadays, thermowood is more and more favourite and used for excellent facilities against biological pests. But also is so important to review it from side of fire protection and safety. Thesis is about effect of thermal treatment of inflammability Sessile Oak (Quercus petraea). The research was conducted on samples without thermal treatment, with thermal treatment 160 degrees 3 and 9 hours and 200 degrees 3 and 9 hours. The Inflammability of samples was presented by flash point and ignition temperature which were fixed by norm STN ISO 871 (2010). You can see from the results, that thermal treatment did not have a significant effect fot thore fire characteristics. Also you can see, that biggest effect has thermal treatment on flash point than ignition temperature, where all samples reached the same value – 400 degres. The flash point is at 330 degrees for samples without heat treatment, for samples with heat treatment at 160 degrees for 3 hours. With other samples were flash point around 340 degrees.