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Abstract: KTa x Nb1− x O3 (KTN) is a promising material for optical devices because of its large electro-optic (EO) effect. Recently, we reported a 2×2 Mach–Zehnder interferometer (MZI)-type EO switch consisting of a single-crystalline KTN waveguide. The development of this switch involved two important breakthroughs in relation to the crystal growth process, namely the successful use of top seeded solution growth (TSSG) and liquid phase epitaxy (LPE). We grew large KTN crystals with the TSSG technique. KTN crystals pulled in the [001] direction are rectangular and surrounded by four {100} facets. We detected faceted striations in the crystals under polarized light. Although there were {100}-, {010}-, and {001}-faceted striations in the initially grown part of the crystals, {001}-faceted striations could only be detected in the later grown parts of the crystals. We confirmed that the crystals exhibited a large EO coefficient of 4.8×10−15 m2/V2, which is the highest value yet reported. We grew epitaxial KTN films using the LPE technique. The crystallinity of the films and their surface flatness were improved by adjusting the growth conditions. The X-ray diffraction (XRD) pattern shows that the films on the KTN substrate were grown epitaxially. Surface flatness measurements showed that the film roughness was less than 0.1μm. We fabricated waveguides by using LPE and additional lithographic processes. The fabricated waveguides achieved single-mode beam propagation, a low propagation loss, and polarization independence. The 2×2 MZI-type EO switch was successfully operated with a very low V of 2.6V. These waveguide and switch characteristics proved that LPE-grown KTN epitaxial films on TSSG-grown KTN substrates have sufficient crystallinity for optical applications. [Copyright &y& Elsevier]