High-quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed-laser deposition. Both, c-axis and a-axis BaTiO3 orientations were studied. Mach–Zehnder optical waveguide modulators with a fork angle of 1.7° have been fabricated by ion-beam etching. The waveguides are of the ridge type, the BaTiO3 thickness is 1 μm, the ridge step 50 nm, and the width 2 μm. Light was coupled into the waveguides from optical fibers. The BaTiO3 waveguide propagation losses are 2–3 dB/cm. Electrodes of 3 mm length were deposited besides the waveguides. Electro-optic modulation has been demonstrated with Vπ = 6.3 V at 632 nm wavelength and Vπ = 9.5 V at 1550 nm wavelength for the a-axis samples, and with Vπ = 8 V at 632 nm wavelength and Vπ = 15 V at 1550 nm for the c-axis samples. Theoretical modelling of the Mach–Zehnder modulators for both crystalline orientations of the BaTiO3 films gave the Pockels coefficients r51 = 80 pm/V for the c-axis film and an effective Pockels coefficient reff = 734 pm/V for the a-axis films at 632 nm wavelength. © 2002 American Institute of Physics.