To clarify the behavior of biomass particles injected into a boiler furnace, the drag coefficients (C-D) for five typical kinds of biomass samples were experimentally examined. It was found that although the shape (length to diameter ratio) of biomass varied with the kind of material, the value of C-D could be approximately arranged by using Reynolds number based on the diameter of a hypothetical sphere with the same volume as the biomass particle. It was also found that the value of C-D for woody biomass particles pulverized to 0.5-8 mm in diameter with an impact mill could be assumed to be that of a cylinder with approximately 0.8 shape factor (phi), and that the value of phi for bark decreased with the particle diameter, even though the external shape was the same as that of the woody portion. The difference of phi seemed to depend on the condition (smooth or fluffy) of the particle surface. When woody biomass was supplied to a coal-fired boiler, the movements and mean temperature of particles were numerically simulated. In the boiler studied here, 20 coal burners (4 corners X 5 vertical stages) were installed. When the biomass particles were injected from three burner stages (upper, middle, and lower), the biomass particles of 3 mm in diameter stayed in the furnace for approximately 2-3 s, 3-4 s, and 5-7 s, respectively, and subsequently flowed to the boiler outlet or dropped to the bottom. By considering these durations together with the calculated temperature history of particles, the pulverizing diameter and burner installation necessary to consume biomass completely within the boiler furnace could be estimated.