An analysis of the nature of anisotropy of the optical properties of LiTaO3 is presented on the basis (of the features) of its intrinsic crystallographical properties. Electrooptically induced refractive-index change in the regular and reverse-poled LiTaO3 is calculated. Specifically we determine how the index change depends on electric field magnitude and direction in y-propagating extraordinary modes. To accomplish this, changes in index-ellipsoid shape and orientation are determined by use of a numerical eigenvalue procedure for diagonalizing the impermeability tensor; then the refractive index is calculated by vector reference-frame transformation and small perturbation approximation. The general formula is inferred from calculations for specific field directions. Electrooptic coefficients for the reverse-poled LiTaO3 are obtained tensor reference-frame transformation of those of LiTaO3.