Miscanthus sinensis was pretreated and used to produce fiberboard with no synthetic binders. The lignocellulosic material was steam exploded with a thermomechanical aqueous vapor process in a batch reactor. The effect of the pretreatment and the pressing conditions on the physicomechanical responses of the fiberboard was evaluated and the conditions that maximize the responses were found. Response surface methodology with a central composite design was used. The variables studied and their respective variation ranges were: pretreatment temperature, 196-236°C; pretreatment time 1-6 min; pressing temperature, 130-230°C; pressing time, 1.6-18.4 min. The boards obtained were of very good quality (modulus of elasticity up to 6070 MPa, modulus of rupture up to 48 MPa, internal bond up to 2.9 MPa, thickness swelling up to 4% and water absorption up to 8%) and more than satisfy the requirements of the relevant standard specifications. The effect of the pretreatment influence on the lignin, cellulose and hemicelluloses content was also determined by a fractionation of the previous experimental design. The decrease in hemicelluloses is clearly related to the increase in the dimensional stability of the boards.