Lead-free (K0.5Na0.5)(Nb0.7Ta0.3)O3 (KNNT) piezoelectric thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by chemical solution deposition method. The effects of annealing temperatures 550, 600, 650, 700, and 750 °C on microstructure, leakage current, ferroelectric, and piezoelectric properties of the KNNT thin films were investigated. The largest remanent polarization Pr (10.5 μC/cm2), piezoelectric coefficient d33 (62 pm/V), and lowest leakage current density (4.6 × 10−6 A/cm2 under 120 kV/cm) of the KNNT film were obtained with annealing at 700 °C. The mechanisms concerning the enhancement in d33 are discussed, and the improved piezoelectric performance of the KNNT film suggests a promising candidate for piezoelectric thin film devices.