The use of heat treatment to modify wood using different treatment heat transfer media, such as nitrogen, vegetable oil, steam, and vacuum, is preferable in many respects to other methods that use chemical treatments. However, the results of the heat treatment differ based on the heat transfer media that are used. In this study, the thermal modification of black pine wood in vacuum, nitrogen, and air atmospheres was studied. The heat treatments were conducted at temperatures of 180 °C, 200 °C, and 220 °C. After the heat treatments, the density, mass loss, modulus of rupture, modulus of elasticity, and impact of bending of heat-treated black pine wood were determined. The results indicated that the density, modulus of rupture, and impact of bending decreased as the temperature increased. In addition, the greatest decrease in the mechanical properties of the wood occurred in the test samples that were treated in air. The vacuum atmosphere was least harmful to the mechanical properties of the wood, and the differences in the mechanical properties of the wood that were heat treated in vacuum and nitrogen were unnoticeable.