Mountain pine beetle (Dendroctonus ponderosae)–infested lodgepole pine (Pinus contorta) bark was used to make particleboard panels (bark board) without synthetic resins. The effects of pressing temperature and particle size on the mechanical properties of the bark boards were examined. The study revealed that pressing temperature and particle size have great influence on mechanical, physical, and hygroscopic properties of self-bonded bark boards. Higher pressing temperatures resulted in improvements in all properties studied, including increases of modulus of elasticity and modulus of rupture by approximately 4 times and an increase of internal bond strength by nearly 10 times when comparing boards pressed at 170°C versus 230°C. Boards produced from fine bark particles showed better mechanical performance than boards produced from coarser bark particles except for internal bond strength, which was highest in boards containing bark particles of mixed sizes. Scanning electron microscopic images of fractured surfaces of bark boards derived from different particle sizes and pressed at different temperatures indicated that fine and mixed particles and higher pressing temperatures led to denser packing.