A property design concept involving the substitution of each crystal site in the pseudoperovskite in Bi₄Ti₃O₁₂ structure, a site-engineered concept, is proposed for Bi₄Ti₃O₁₂-based thin films. This concept is based on the selective substitution of each crystal site contributing to the ferroelectric properties. By using this concept, a novel material, i.e., (Bi, Nd)₄Ti₃O₁₂ was developed. A spontaneous polarization (P_s) value was 58 μC/cm² beyond the single crystal data of Bi₄Ti₃O₁₂. In addition, taking account of the realizable orientation of the film on (100)Si substrate, the expected remanent polarization (P_r) value of (Bi_3.5Nd_0.5)Ti₃O₁₂ film is almost the same with those of widely-used Pb(Zr_0.35Ti_0.65)O₃ films.