In many practical applications, piezoelectric devices are driven under strong electric field or under DC bias field. To evaluate the performance of the piezoelectric devices under these strong field conditions, the materials constants measured under weak field are usually not applicable. In this paper, we report our measurement results on the effect of DC bias field on the complex piezoelectric, dielectric and elastic coefficients of piezoelectric lead zirconate titanate ceramic resonator. A thin plate soft PZT resonator (transverse mode) is used in this study. A recently developed accurate method is used to directly characterize the complex materials coefficients, in which for a thin plate PZT resonator with length extensional vibration mode, normalized electric admittance, (=Y/ω) instead of admittance Y spectrum is used to determine the materials coefficients under various DC bias fields applied along the polarization direction. It has been found that with DC bias field increasing, elastic compliance, piezoelectric coefficient and dielectric permittivity decrease with approximately linear relationships. Second-order electromechanical coefficients can be estimated through the measurement of materials coefficients under DC bias conditions. Based on the observation of frequency increasing with DC bias field, it is suggested that the DC bias field can be used for frequency tuning or frequency–temperature compensation.