Epitaxial tetragonal tungsten-bronze structure Sr1.8Ca0.2NaNb5O15 (SCNN) thin films of 650 nm thick have been grown on Si(0 0 1) substrates for the first time using pulsed laser deposition. The large lattice mismatch between SCNN films and Si substrates was overcome by making use of a MgO/TiN buffer layer. Excellent optical waveguiding properties of these SCNN films have been demonstrated using a prism-coupling technique. The ordinary and extraordinary refractive indices at 632.8 nm were calculated to be 2.2141 and 2.1727, respectively, implying a large birefringence of 0.0414. A propagation loss of 1.7 dB cm−1 was measured in our waveguides. Our studies suggest that the SCNN/MgO/TiN/Si heterostructure is an ideal candidate for integrated optical waveguide applications.