Constitutive relations of ferroelectric composites with a transformable partially stabilized–zirconia (PSZ) matrix are developed based on the mean field theory. The effect of phase transformation of the matrix on the electromechanical coupling behaviour is highlighted. The general constitutive relations are specialized to a model ferroelectric composite in which lead–zirconate–titanate (PZT) inclusions are oriented in three mutually orthogonal directions, in order to illustrate the interaction. The analysis shows that if the composite is partly or completely polarized, t → m phase transformation can be induced by an applied electric field due to electromechanical coupling. t → m phase transformation can increase the toughness of the ferroelectric composite if the absolute values of the residual stress/strain and the residual electric displacement in the composite after the t m phase transformation are larger than those before it.