Heat treatment improves dimensional stability of wood, reduces its decay, and darkens its color. However, mechanical properties of wood can deteriorate during the heat treatment. The effect of heat-treatment conditions (maximum treatment temperature, heating rate, exposure time at the maximum heat-treatment temperature, and the gas humidity) on the mechanical properties of North American jack pine (Pinus banksiana) was studied using thermogravimetric analyzer. This type of study permits the identification of the best treatment conditions which will minimize reduction of mechanical properties of jack pine. The results showed that the degree of change in bending strength, hardness, screw withdrawal strength, and dimensional stability of jack pine during heat treatment depends strongly on the treatment conditions used. Therefore, great care should be taken to select the treatment conditions. Thermogravimetric analysis can be used as a first step for selection.