Mechanical parameters of ash wood (Fraxinus excelsior) subjected to compression in tangential direction, before and after its thermal modification and measured at the moisture content close to the equilibrium moisture content of wood used inside and outside the house, (4 and 12%) were compared. Thermal modification of wood was performed at 190°C and 200°C for 2 hours in industrial conditions. During the measurements, the moisture content of the modified and control samples was the same. The parameters compared included: modulus of elasticity, stress at proportionality limit, relative linear strain at proportionality limit and accumulated elastic energy. Thermal modification of ash wood at 190°C contributed to the deterioration of its mechanical parameters determined during compression in tangential direction; the deterioration was greater for wood tissue of higher moisture content. The values of mechanical parameters of thermally modified wood (except for elastic energy), determined in compression test in tangential direction, decrease with the its increasing moisture more than for the control wood
