We have fabricated K_0.5Na_0.5NbO₃ (KNN) thin films on Pt substrates by a chemical solution deposition method and investigated the effect of K and Na excess (0–30 mol %) for KNN thin film. The KNN film with 20 mol % excess K and Na was an optimized KNN perovskite phase. From the Raman spectra, a change in the scattering mode was observed due to the chemical composition fluctuations of the excess K and Na. The peak of the (v ₁ + v ₅) internal vibrational mode in the NbO₆ octahedra was split into two vibration modes which were shifted toward lower or higher wavenumbers depending on the K and Na cation deficiencies or redundancies.