ZrO2 and its modified versions containing MgO and Y2O3 were selected as particulate reinforcement in order to achieve better mechanical properties of mullite. Particulate composites up to 25 vol% ZrO2 and its modifications were pressed to 55% relative density at 300 MPa followed by sintering at 1600 degrees C and 1650 degrees C for one hour. Studies were conducted on fracture toughness, transverse rupture strength, hardness, dielectric constant, microstructure and fractography. Composites sintered at 1650 degrees C were found superior in properties than those at 1600 degrees C. The maximum strength of mullite composites was observed at a composition of 10 vol% ZrO2.