Optical waveguides were successfully fabricated by femtosecond laser direct writing inside a LiTaO3 crystal, and the optical properties of these waveguides were investigated. Optimum writing conditions such as pulse energy and duration were determined on the basis of the refractive index changes calculated using the near-field pattern of the light guided through the waveguides. μ-Raman spectroscopy results and birefringence observations around the formed waveguides suggested that the local increase in refractive index was caused by anisotropic compressive stress in the laser-irradiated region. The light guided through the formed waveguide showed strong polarization dependence. © 2011 Ceramic Society of Japan.