Pb(Zr, Ti)O (PZT) has been the most widely utilized in piezoelectric Micro Electro Mechanical Systems (MEMS) actuator. However, the improvement of its piezoelectricity has been saturated recently. Thus, we have developed Sm-doped Pb(Mg, Nb)O3-PbTiO (Sm-PMN-PT) epitaxial thin film as a next-generation piezoelectric thin film beyond PZT. In this study, a (001)/(100)-oriented Sm-PMN-PT with the pure perovskite phase was successfully sputter-deposited on a Si substrate using an epitaxial PZT buffer layer. The transverse piezoelectric coefficient, |e|, of a 1.5-gm-thick Sm-PMN-PT/PZT stack film measured over 20 C/m, which is equivalent to or better than those of the best class PZT thin films. From this result, the influence of the PZT buffer layer was deembedded, and |e| of the sole Sm-PMN-PT thin film was estimated at higher than 26 C/m. This result suggests a potential of epitaxial Sm-PMN-PT for high-performance piezo-MEMS.