Lithium diffusion in lithium niobate crystals with different initial Li2O content (C-initial) was investigated under Li-rich environment at 1100 degrees C. Lithium niobate crystals with widely varying diffusion-limited Li2O content profiles were prepared through the vapor transport equilibration (VTE) technique using congruent lithium niobate crystals with different C-initial, and the profiles were measured through Curie temperature by a thermal analyzer. A Boltzmann-Matano analysis was employed to those profiles to estimate the Li+ diffusivity as a function of Li2O content in lithium niobate crystals. A trigonometric function method was applied to those profiles to correlate diffusion time and Li2O content. The results show that at the same composition of lithium niobate crystals after diffusing treatment, the less the C-initial, the larger the Li+ diffusivity. The relation between diffusion time and Li2O content of the samples which have different C-initial and thickness was derived. Based upon the Boltzmann-Matano result, diffusion time can be estimated easily from the relation. It is concluded that increasing C-initial contributes to shorten the diffusion time for preparing near-stoichiometric lithium niobate crystals through the VTE technique, especially for thick crystal wafers.