Four kinds of unpoled lead zirconate titanate (PZT95/5) ferroelectric ceramics were fabricated in a range of different porosity levels by systematic additions of added pore formers. By using the non-contact digital image correlation (DIC) optical technique to measure the full-field strain, the response of unpoled PZT95/5 ferroelectric ceramics to statically applied uniaxial stresses was investigated. The influences of porosities on the mechanical behavior, domain switching, and phase transformation of the porous unpoled PZT95/5 ferroelectric ceramics were explored. All the measured stress versus strain curves for the tested porous unpoled PZT95/5 ferroelectric ceramic samples can be divided into three stages: the initial linear elastic region, the approximate plateau region, and the second linear elastic region, similar to the behavior of foam or honeycomb materials. However, the deformation mechanism of porous unpoled PZT95/5 ferroelectric ceramics should be attributed to the domain switching and phase transformation processes, but not related to the collapse of voids. With the increase of porosity, the elastic modulus, fracture strength and fracture strain of the porous unpoled PZT95/5 ferroelectric ceramics would decrease. Effect of dispersed voids does not improve plasticity of the porous unpoled PZT95/5 ferroelectric ceramics, which is mainly attributed to no effect of the pores on the obstacle and proliferation of crack propagation during the axial splitting failure processes. Critical stresses of the domain switching and phase transformation decrease linearly with increasing porosity. The macroscopic critical volumetric strain needed for phase transformation is independent of the porosity in the unpoled PZT95/5 ferroelectric ceramics.