Lead-free Sr2KxNa1-xNb5O15 (0.00 <= x <= 0.20) piezoelectric ceramics were prepared by two-step solid state reaction method. Pure tungsten bronze structure could be obtained in all ceramics and K substitution could accelerate the phase formation at lower temperatures. The lattice constant calculation indicated expansion of the unit cell and reduced distortion of the crystal structure with K substitution due to the bigger ionic size of K+ (1.64 angstrom) compared to that of Na+ (1.39 angstrom). Electrical properties of Sr2KxNa1-xNb5O15 ceramics greatly depended on the K content. Curie temperature T-c shifted downward, whereas the maximum dielectric constant epsilon(m) and the degree of diffusion phase transition all increased initially and then decreased as K content increased, indicating that proper amount of K substitution with x between 0.05 and 0.10 could enhance the dielectric properties. All the ceramics showed an intermediate relaxor-like behavior between normal and ideal relaxor ferroelectrics according to the modified Curie-Weiss law. With increasing K content, the remnant polarization (P-r) decreased gradually and the coercive field (E-c) decreased initially and then increased. But normal ferroelectric hysteresis loops could be observed in all compositions. Besides, the underlying mechanism for variations of the electrical properties due to K substitution was explained in this work. (C) 2011 Elsevier B.V. All rights reserved.