Herein, the results of systematic mechanical property measurements of pressureless sintered calcium phosphate (CaP)-mullite composites are discussed. Our experimental results demonstrated how the mullite addition (upto 30 wt%) influenced hardness, elastic modulus, strength and toughness properties of the composites. In assessing each of these fundamental material properties, either a range of load or a number of complimentary techniques were used to obtain reliable measure of mechanical properties. Importantly, the results of single edge V notch beam measurements revealed that a reliable toughness value of ~1.5 MPa m(0.5) could be obtained in composites containing 20 or 30 wt% mullite. Our results clearly illustrated that a combination of elastic modulus (~80 GPa), compressive strength of more than 350 MPa, three-point flexural strength of 70-80 MPa, hardness of 4-5 GPa were achievable with the investigated composites. Such a combination of material properties, in addition to modest toughness property appeared to indicate that CaP-mullite composites could be used as a biomaterial for hard tissue replacement.