We report a comparative study of the dielectric properties of solid-state (ceramic method) synthesized NaNbO3 (NN), Na0.75K0.25NbO3 (K25NN), K0.5Na0.5NbO3 (KNN) and some composite materials containing In2O3 and NN or KNN using an AC impedance method. Powder X-ray diffraction (PXRD) was employed to investigate the phase purity. No significant amount Of impurity phase was observed for NN, K25NN, and KNN. Substitutions of 10, 15 and 25 mol% In3+ for Nb5+ in KNN and NN using solid-state reactions at 1150 degrees C resulted in composite materials. AC impedance studies of NN, KNN and K25NN in the temperature range of 500-800 degrees C showed a single semicircle (attributed to the bulk property) in the high-frequency range of 10(3) to 10(6) Hz. The individual contributions from the bulk and grain boundary on the dielectric properties were resolved and quantified from the impedance data. The calculated dielectric Values for NN were consistent with previously reported in the literature. 10% Indium based KNN composite materials had the lowest dielectric loss 0.585 and the dielectric constant of 233 at 100 kHz at the temperature of 650 degrees C. (C) 2008 Elsevier Ltd. All rights reserved.