Na0.5K0.5NbO3 (NKN) and 10mol% (Na,K) excess Na0.5K0.5NbO3 (NKN10) thin films on Pt/Ti/SiO2/Si substrate were prepared by chemical solution deposition. Crystallization of NKN10 thin films was confirmed by X-ray diffraction. The (Na,K) excess Na0.5K0.5NbO3 thin film shows a ferroelectric P-E hysteresis loop. Dielectric properties and impedance spectroscopy of thin films were investigated in the frequency range from 0.1Hz to 100kHz and the temperature range of 25~500°C. By analyzing the complex impedance relaxation with Cole-Cole plots, we found impedance relaxations for the thin film. The contribution of electrical conduction is discussed in relation to grain, grain boundary, and interface effects.