Replacing bone in load bearing sites still poses a challenge. Fiber reinforcement of calcium phosphate based cements is a promising strategy to develop bone substitutes with improved mechanical properties. In this study, the reinforcement of calcium phosphate cement (CPC) and sodium-magnesium phosphate cement (MPC) is investigated. Polylactic acid (PLA) fibres with two different diameters (18 μm and 50 μm) were employed to create biocompatible and resorbable composites with superior mechanical properties. The main focus in this study was to evaluate the potential effect of low temperature plasma treatments on the reinforcing capacity of the fibres and the fibre-matrix interactions. The influence of various gases, as well as the treatment time were investigated for the low temperature plasma treatments. The effect of the plasma treatment on the wettability of the fibres was investigated by capillarity and contact angle experiments and the topography was analysed by scanning electron microscopy. A single fibre pull-out experiment was designed, using PLA fibres with a diameter of 150 μm. to investigate the interfacial shear strength of the fibre-matrix interface for the two cement types and the different plasma treatments. The mechanical properties were investigated by means of three-point bending experiments. The elastic modulus, flexural strength and work of fracture were evaluated and compared for the different cement types and different fibres, as well as for untreated and plasma treated fibres. The work of fracture increased significantly for composites with thick fibres, while their strength and the elastic modulus only increased slightly. An improvement in the mechanical properties for plasma treated PLA fibres was observed for both cement types, the effect being more significant for the thick than for the thin fibres. Overall, stronger and tougher composites were developed, compared with similar materials reported in the literature. Finally, a first attempt to incorporate PLA fibres into magnesium phosphate cements was undertaken. The fibre reinforced cements exhibited improved bending strength and toughness compared to the pure cement. However, the pure MPC cement exhibited very poor mechanical properties in bending and the MPC/PLA composite still exhibited inferior properties compared to the presented CPC/PLA composite.