Thermal modification of wood is an environmentally friendly alternative to other preservative treatments which provides improvement in durability and dimensional stability. Heat treatments have been mainly applied to softwoods for non-structural uses. Considering the current abundance of hardwoods such as beech, heat treatment becomes a way to add value to this species through the development of new engineering products. In this sense, any theoretical model for structural analysis purposes requires the implementation of the material elastic stiffness constants. The work here presented focuses on the experimental characterization of the linear elastic orthotropic behaviour of thermally modified beech to three different heating temperatures. The tests are carried out by non-destructive ultrasound technique in difference to the mechanical processes conventionally applied to this end.