A simple preparation of KNbO3 powders was proposed by an alternative approach of solid-state reaction. Stoichiometric niobium oxalate and potassium acetate were mixed in water and then dried. It was demonstrated that an ion-exchange reaction occurred with the formation of K[NbO(C2O4)(2)]center dot nH(2)O intermediate. The single-phase KNbO3 powders were synthesized when K[NbO(C2O4)(2)]center dot nH(2)O intermediate was calcined between 500 and 800 degrees C for 3 h. KNbO3 powders obtained at 500 degrees C are determined as orthorhombic structure with an average particle size of 20-50 nm by X-ray diffraction, scanning electron microscope (SEM), and transmission electron microscopy (TEM) analysis. The morphologies of KNbO3 obtained at different temperatures were observed by SEM and TEM analysis. The average band gap energy is estimated to be 3.16 eV by UV-vis diffuse reflectance spectra.