Lead zirconate titanate (PZT) based composites were prepared from commercially available PZT powder and a small amount (0.1 - 1.0vol%) of nano-sized alumina or magnesia, and their mechanical and piezoelectric properties were evaluated. The fracture strength of the composites increased with increasing second phase content due to grain size reduction, particularly in the case of PZT/MgO composites, which showed a significant improvement in strength. The planar electromechanical coupling factor, Kp, of the composites remained unchanged. As a consequence, highly reliable PZT composites with high strength (140 MPa) and Kp (60%) have been fabricated.