A Miscanthus Sinensis plantation in Galicia, Spain, provided the raw material for experimental fiberboards. After harvesting, the Miscanthus stems were cleaned and chipped. The chips were steam exploded with a thermomechanical aqueous vapor process in a batch reactor. The resulting material was dried, slightly milled, and used to produce fiberboard with no synthetic binders. The pretreatment and the pressing conditions that optimize the physico-mechanical responses were determined. Response surface methodology with a central composite design was used. The variables studied and their respective variation ranges were: pretreatment time, 4-14 min; pressing temperature, 195-245°C; pressing pressure, 1.9-14.6 MPa. The boards obtained were very good quality (modulus of elasticity as high as 7630 MPa, modulus of rupture as high as 61 MPa, internal bond as high as 4.1 MPa, thickness swelling as low as 2.5%, and water absorption as low as 8.9%) and more than satisfied the requirements of the relevant standard specifications.