We fabricated Bi0.5(Na0.85K0.15)0.5TiO3 (BNKT) lead-free thin films on Pt(111)/TiO2/SiO2/Si(100) substrates by using a chemical solution deposition method. The BNKT thin films were annealed at 650, 700, 750, or 800 °C in an O2 atmosphere. X-ray diffraction patterns revealed a pure perovskite structure at annealing temperatures from 650 to 800 °C. A field emission electron microscope study revealed an increase in grain size with increasing annealing temperature. BNKT thin films annealed at 700 °C had a high remnant effective piezoelectric coefficient of 63.6 pm/V and a low leakage current density of 5.15 × 10−6 A/cm2.