An analysis of the nature of anisotropy of optical properties of LiTaO3 is presented on basis of features of its intrinsic crystallographical properties. Electro-optically induced refractive-index change in regular and reverse-poled LiTaO3 has been calculated. Specifically we determine how index change depends on electric field magnitude and direction for y-propagating extra-ordinary modes. To accomplish this, changes in index-ellipsoid shape and orientation are found by the use of a numerical eigenvalue procedure to diagonalize the impermeability tensor; then the refractive index is calculated by the use of a vector reference-frame transformation and a small perturbation approximation. A general formula is inferred from calculations for specific field directions. Electro-optic coefficients for reverse-poled LiTaO3 are obtained by application of a tensor reference-frame transformation to those of LiTaO3 .