(In0.5Nb0.5)(0.005)(Ti1-xZrx)(0.995)O-2 (INZT, x = 0-0.10) ceramics were synthesized using a conventional sintering method, and the effects of Zr content on the microstructures, dielectric properties and electron-pinned defect-dipoles (EPDD) polarization of the resultant products were investigated. The solubility limit of INZT was x = 0.075, and a secondary ZrTiO4 phase appeared at x = 0.10. Ceramics with x = 0-0.10 exhibited excellent dielectric properties, ie, colossal permittivity (CP, epsilon MODIFIER LETTER PRIME > 10(3)) and low dielectric loss (tan delta < 0.1), over a wide range of frequencies (10(0)-10(6) Hz at 300 K) and temperatures (50-350 K at 1 kHz). The dielectric spectra and XPS results confirmed that the CP property of the ceramics could be ascribed to their EPDD polarization. The activation energy (E-a) for EPDD polarization was continuously enhanced by increasing x values. EPDD relaxation parameters at different x values were revealed using Cole-Cole equation fitting. Moreover, alpha, which characterize the relaxation time tau distribution, increased with x values, thus indicating that Zr was involved in and affected electron localized states. The high E-a, temperature T-p of the peak epsilon MODIFIER LETTER PRIMEMODIFIER LETTER PRIME at 1 kHz, and dielectric relaxation time tau(p) at 30 K were related to increases in hopping distance of electrons among defect clusters with Zr addition.