Temperature stabilities of dielectric constants and resonance frequencies of the substrates are very important in piezoelectric ceramic oscillators and filters. In this study, it was investigated temperature stability of the length-extensional vibration mode of Pb(ZryTi1-y)O-3 + x(wt.%)Cr2O3 ceramics. Addition of Cr2O3 in morphotrophic phase PZT decreased the variations of the dielectric constant and the resonance frequency by thermal shock, As additive weight of Cr2O3 increased in morphotrophic phase composition y = 0.53, the temperature coefficient of resonance frequency changed from positive number to negative one. The thermal aging process shifted the point with the zero temperature coefficient of resonance frequency to be placed at the composition with much higher Cr2O3 additive weight in PZT ceramics. (C) 2004 Published by Elsevier B.V.