Aluminium nitride-molybdenum ceramic matrix composites are produced by hotpressing a mixture of two powders. Mechanical properties of a series of samples are measured in order to study the effect of molybdenum phase on the behaviour of composite. Th ree-point bend strength increases from a value of 270 MPa for pure aluminium nitride to 571 MPa for a composite containing 40% by volume of metallic phase. Fracture toughness measured by the single-edged precracked beam (SEPB) technique, is also increased as a function of molybdenum concentration. From 2.3 MPam(1/2) for pure AlN we obtain a value of 6.9 MPam(1/2) in the case of composite containing 40% by volume of metallic phase. This very important increase in the mechanical properties of AlN-Mo composites is attributed to higher mechanical properties of molybdenum and an adherent interface between AlN and Mo grains.