We present a new wavelength and temperature dependent refractive index equations for 0.5% MgO doped periodically poled stoichiometric LiTaO 3 crystal for both extra-ordinary and ordinary polarizations. Our equations fit experimental data over a wide temperature (25-250°C) and spectral ranges: 0.35-6 ¿m for the extra-ordinary wave and 0.375-3.75 ¿m for the ordinary wave. The equations were cross validated with measurements of o-eo and e-oo interactions, involving both ordinary and extra-ordinary refractive indices. These dispersion equations are based on new measurements data derived from quasi phase matched frequency conversion experiments, and they are also in good agreement with previously published data.