The dependence of the mechanical properties such as strength, modulus and fracture toughness on the volume fraction of the reinforcing glass fibres and glass beads in polyoxymethylene (POM) matrix was studied. The majority of the measured quantities in tension or flexure tests, seemed to be linear functions of either the volume fraction of the glass fibres or the glass beads. The relationship between some individual mechanical properties seemed to be linear as well. Consequently, many of the mechanical properties of these POM composites (POM/GF and POM/GB) could be estimated from one measured property using the relationships presented. Also, the same property measured for the two composite systems was found to be linearly related. Consequently, the mechanical properties of one composite system, (i.e. POM/GB) could be used to determine that of the other system (i.e. POM/GF) at the same filler concentration.