K0.5Na0.5NbO3-xSrTiO(3)(x = 0, 0.1 and 0.2) ceramics were prepared using the solid-state method. The phase transition behaviors, electrical properties, and electric field-induced dielectric nonlinearity behaviors were investigated as a function of the SrTiO3 content. The electrical properties of the investigated compositions exhibited a significant dependence on the content of SrTiO3. Doped content more than x = 0.1 induced a relaxor transformation, while the dielectric loss decreased quickly. In addition, an "extrinsic" polarization contributed to the dielectric nonlinearity behavior of the composition x = 0.1 with the polar nanoregions and domain-wall motions, by means of the multipolarization-mechanism model fittings of the electric field dependence of the dielectric permittivity. The dielectric tunability and loss angle tangent of the composition x = 0.1 were 32.6 % and 0.028, respectively.