Lead-free ferroelectric ceramics of (1-x) [0.88Na(0.5)Bi(0.5)TiO(3)-0.12K(0.5)Bi(0.5)TiO(3)]-x KNbO3 (x = 0, 0.02, 0.04, and 0.06) were prepared by the conventional ceramic fabrication technique. The crystal structure, dielectric properties and P-E hysteresis loops were investigated. XRD data showed that all compositions could form pure perovskite structure. Temperature dependence of dielectric constant epsilon(r) and dissipation factor tan delta measurement between room temperature and 500 degrees C revealed that the compounds experience phase transitions that from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric in the range of x = 0-0.04. The frequency dependent dielectric constant showed these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant and dissipation factor increased sharply attributed to the superparaelectric clusters after the KNbO3 doped. (c) 2005 Springer Science + Business Media, Inc.