Miscanthus sinensis was thermomechanically pretreated and used to produce fiberboard with no synthetic binders. The lignocellulosic material was steam exploded using an aqueous vapor process in a batch reactor. Part of the resultant pulp was ground to pass through a 4-mm sieve. The effect of the grinding on the physicomechanical responses of the fiberboard was evaluated. ANOVA methodology was used. The boards obtained with the ground pulp were of better quality that those obtained with the non-ground pulp. The milling process considerably improved the internal bond strength and diminished the density of the board. The other measured properties (MOE, MOR, WA and TS) were not significantly affected by the process. Scanning electron micrographs show that the changes are due to the segregation of packages of fibers and not to the cut of the fibers. This segregation increases the inter-fiber bonding area.