Lead-free (K0.48Na0.48Li0.04)(Nb0.995−xMn0.005Tax)O3 (abbreviated KNL-NMT-x, x = 0 ∼ 0.20) thin films were prepared using a chemical solution deposition method, and the effects of Ta content on the structural, dielectric, ferroelectric, and piezoelectric properties were investigated. X ray diffraction results indicate that the phase structure of KNL-NMT-x films undergoes a transition from orthorhombic to pseudocubic phase with increasing Ta content. The substitution of Ta5+ for the Nb5+ site in the KNL-NMT-x films produced to the relaxor-like ferroelectric with a diffuse phase transition. The KNL-NMT-0.10 thin film at the orthorhombic-pseudocubic phase boundary showed optimum dielectric and piezoelectric properties; dielectric constant ɛr = 2650, Curie temperature Tc = 323 °C, remnant polarization Pr = 16.1 μC/cm2, coercive field Ec = 22.2 kV/cm, and effective piezoelectric coefficient d33,f = 61 pm/V.