Aspen was heat-treated at high temperature in a laboratory thermogravimetric analyzer. The high temperature wood treatment technology is new in North America and needs to be adapted to the North American species. The objective of this study is to understand how the treatment affects the mechanical properties of aspen such as hardness, modulus of elasticity and modulus of rupture, and, consequently, the quality of the product. The wood samples were heated in an inert gas environment under different operating conditions. The parameters studied are the final treatment temperature, heating rate, holding time, and the gas humidity. The weight loss and the temperature history of wood were monitored during the treatment. After the experiments, the properties of the samples were measured, and the effects of the above parameters on the properties were analyzed. The weight loss increased with increasing temperature, heating rate, holding time, and gas humidity. Increasing temperature caused an increase in MOE and a decrease in MOR. Overall hardness decreased with increasing temperature above 160 degrees C and it increased with increasing holding time and heating rate whereas it decreased with increasing gas humidity. Holding time and heating rate did not seem to affect MOE. Gas humidity increased MOE. MOR increased with holding time and decreased with heating rate and gas humidity.