The non-linear piezoelectricity of multilayer ceramic actuators (MCA) using PMN-PZT ceramics was investigated under the combined loading of electric field and compressive stress. These piezoelectric actuators present the non-linear ferroelectric behaviors. When electric field and compressive stress are simultaneously applied to the ceramics, the ferroelectricity is expected to be different from that of ceramics induced by only one quantity, electric field or mechanical load. This property difference was estimated via piezoelectric equation. Unlike the case of application of only one inducing quantity, electric field or mechanical stress, the piezoelectric and dielectric behavior was found to be strongly dependent upon variation in dielectric permittivity under the mechanical loading. (c) 2004 Elsevier B.V. All rights reserved.