Four species of wood: two softwoods (Douglas-fir and pine) and two hardwoods (aspen and hybrid poplar) are investigated for their size reduction energy consumption and ground particles size distributions. Lignin content, ash content, and density of wood is measured. Specific grinding energy was 155.9, 226.1, 209.1, and 276.3 kJ/kg for Douglas-fir, pine, aspen, and hybrid poplar, respectively. The analysis of variance shows that lignin content (ranged from 26 to 36.7 %wt based on oven-dry, extractive-free wood) and ash content (ranged from 0.36 to 0.55 % wt dry basis) are significant factors on effective energy consumption of grinding.