Binderless boards were manufactured from rice straw by hot-pressing in order to evaluate the morphoogical effect of particles from rice straw. For the morphological effect, we examined the influence of particle size and morphological parts of rice straw, respectively. Internal bonding (IB), thickness swelling (TS) and water absorption (WA) were measured as the properties of the boards. As a result, binderless boards were successfully manufactured from rice straw powder smaller than 1 mm. Regarding the effect of morphological part from rice straw, IB of the board made from stem powder was the highest, subsequently followed by leaf blade powder, and leaf sheath powder. IB tended to increase with decreasing ash and silica contents. Trichomes and wartlike protuberances on the epidermis of rice straw might inhibit the bonding between particles. The water resistance of binderless boards made from rice straw was high regardless of low IB. It is possible that waxlike substances on the epidermis of rice straw might contribute to the water resistance of the board.