The work presented here discussed the fiber reinforcement of MDF materials prepared from ordinary portland cements. The effects of fiber type, size and amount on the properties of the ordinary portland cement (OPC)-based macro-defect-free composites were investigated and the toughening mechanism was studied. The potential for increased toughness by fiber reinforcement of MDF composite has been shown. Carbon and Saffil (alumina) fiber reinforced MDF cement composites indicate high mechanical properties (127MPa in modulus of rupture and 3.3MPa⋅m^1/2 in K_1c) and their optimum fiber loading shows 10-15% by volume when a high shear mixing and extruding process were employed.