A series of polycrystalline spinel ferrites with the composition NiInxFe2-xO4 (0 <= x <= 0.3) were prepared by the solid state reaction to study the effect of In3+ ions substitution on their dc electrical resistivity and dielectric properties. The dc resistivity has been investigated as a function of temperature and composition. The indium ion increases the dc resistivity and activation energy of the system. A study of the dielectric properties of these mixed ferrites, as a function of composition, frequency and temperature, has been undertaken. The dielectric constant (epsilon'). dielectric loss (epsilon '') and dielectric loss tangent (tan delta) all decreases with frequency as well as with the composition. The dielectric constant (epsilon') and dielectric loss tangent (tan delta) were increases with increasing temperature. AC conductivity increases with increase in applied frequency. The dielectric behavior of the present samples is attributed to the Maxwell-Wagner type interfacial polarization. The conduction mechanism in these ferrites is due to electron hopping between Fe2+ and Fe3+ ions on adjacent octahedral sites. (C) 2011 Elsevier B.V. All rights reserved.