The epitaxial growth and formation mechanism of the partially La- and Nd-substituted perovskite structures, and the ferroelectric properties of bismuth lanthanoid nickel titanate [(Bi1-xLax)(Ni0.5Ti0.5)O3; BLNT and (Bi1-xNdx)(Ni0.5Ti0.5)O3; BNNT] based solid solution films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction, transmission electron microscope, and polarization–electric field hysteresis loop measurements. BLNT samples at x≥0.3 and BNNT samples at x≥0.4 were confirmed to have a single-phase perovskite structure. This small difference is speculated that it is related to metal–oxygen bond dissociation energy. The sample substituted with La exhibited the best hysteresis loop at x = 0.5 with a remanent polarization of Pr = 12 µC/cm2 and the sample substituted by Nd exhibited the best hysteresis loop at x = 0.4 with a remanent polarization of Pr = 2 µC/cm2.