In-plane ferroelectric polarization in BaTiO3 (BTO) epitaxial thin films on MgAl2O4(001) (MAO) is reported. The directional dependence of both in-plane polarization curves and Raman spectroscopy shows that the films have an orthorhombic structure at room temperature, in contrast to the tetragonal structure of the corresponding bulk. The largest in-plane polarization value among BTO-based tensile-strained films is obtained. The temperature dependence of the lattice constants shows that the Curie temperature of the thin films is as high as 220 °C, which is higher than that of the bulk by 100 °C. The significant enhancement of the Curie temperature is attributed to high-quality coherent epitaxial growth due to perfect matching between the lattice parameter of the c-axis of BTO and that of MAO.