We demonstrate a significant improvement in the epitaxial growth of perovskite dielectric films on MgO by introducing a SrTiO3 (STO)/TiO2 buffer layer, which enhances their dielectric response. 270-nm-thick (001)-epitaxial (Ba, Sr) TiO3 (BST) films were deposited by pulsed laser deposition on STO/TiO2-buffered MgO with a SrRuO3 (SRO) bottom electrode. The film directly deposited on SRO/MgO grew in a three-dimensional mode, resulting in a rough and poorly crystalline film with an almost relaxed strain. On the other hand, the film with a buffer layer grew in a two-dimensional mode, resulting in a flat and highly crystalline film with a large compressive strain (-0.80%). As a result, the paraelectric-to-ferroelectric phase transition temperature increased by 220 degrees C and an out-of-plane dielectric constant exceeding 1000 was achieved. (C) 2018 The Japan Society of Applied Physics