Lead-free Bi 0.5 (Na 0.8 K 0.2 ) 0.5 TiO 3 (abbreviated as BNKT) films have been synthesized via a sol-gel technique on Pt/Ti/SiO 2 /Si substrates, and the dependence of the physical properties in BNKT films were investigated as a function of the crystallization temperature. The BNKT films were annealed at different temperatures (600, 650, 700, and 750°C) for 60 min in the air. The results of this study showed that the optimal crystallization temperature is 700°C. At this, the BNKT films exhibited a single perovskite phase structure and high-dense surface. Besides, the remanent (P r ) and maximum (P m ) polarization reached their highest values of 9.2 μC/cm 2 and 30.6 μC/cm 2 , respectively. All the films showed a weak ferromagnetic behavior with the maximum saturated magnetization (M s ) of 2.1 emu/cm 3 . These values are equivalent to the highest P r and P m values in previous reports on lead-free films.