The thermal modification of wood is well known and widespread as method to improve the dimensional stability and natural durability of this interesting material with biological origin. This work aims to evaluate the effect of a 3 hour at 215°C thermal modification cycle, carried out with an industrial system with a slight initial vacuum, on some physical properties of ayous wood (Triplochiton scleroxylon K. Schum). This research will offer an overview on the dimensional stability and the water absorption behaviour of the material, comparing these properties between untreated and heat-treated ayous wood. To collect the data, the ISO reference standard was adopted. The data here presented highlight the influence of the thermal modification in the reduction of wood hygroscopicity. It has been possible to verify that heat-treated wood shows less swelling and reaches a lower humidity than untreated wood with the same environmental conditions. Therefore, the dimensional stability of the heat-treated wood was also improved, making the material more suitable for outdoor use.