Octahedral lattice sites of Pb[(Zn1/3Nb2/3),Ti]O-3 were replaced by 20 at.% Mg1/3Ta2/3 complex to enhance perovskite development, especially at Pb(Zn1/3Nb2/3)O-3-rich compositions. Resultant changes in the perovskite formation and associated dielectric responses were investigated. A perovskite structure was identified at Pb(Zn1/3Nb2/3)O-3-rich compositions by X-ray diffraction, although the development was rather incomplete. Phase transition modes in the dielectric constant spectra changed from diffuse to sharp ones, regardless of the introduction of Mg1/3Ta2/3. Dielectric maximum temperatures of the ceramics shifted linearly with the compositional change.