Lead-free K0.5Na0.5NbO3–Bi0.5Na0.5TiO3 (KNN–BNT) 0–3 composite ferroelectric thick films have been successfully prepared by a modified composite sol–gel process. The KNN fine ceramic powders were dispersed in the BNT precursor solution to form the uniform slurry that was spin coated on (111) Pt/TiO2/SiO2/Si substrates. The buffer layers and vacuum infiltration were used during the deposition process to improve the structure and density of the composite films. Influence of the annealing temperature and weight ratio of the powder-to-solution on the structures and electrical properties of KNN–BNT composite thick films has been investigated. X-ray diffraction analysis indicates that the composite thick films possess pure perovskite structures composed by KNN and BNT phases. The dielectric constant and remnant polarization of the composite thick films increase with increasing annealing temperature and decreasing powder-to-solution weight ratio due to reduction of pores and improvement of film density. The composite thick films with the powder-to-solution weight ratio of 0.40 and annealed at 750°C have a dielectric constant of 848 and a remnant polarization of 23.6 μC/cm2. The KNN–BNT composite thick films obtained are a promising candidate for transducer applications.