Diffusivity at 1130°C of Li+ in LiNbO3 crystal in off‐congruent, Li‐deficient regime has been studied as a function of Li2O‐content. A diffusion‐limited Li2O‐content reduction depth profile in an X‐ or Z‐cut plate, ranging from 47.2 to 48.5 mol%, was produced by carrying out Li‐poor vapor transport equilibration (VTE) treatment on 1‐mm‐thick, initially congruent plates at 1130°C for 150 h. The profile was obtained by alternatively doing the optical polish to one crystal surface and the Li2O‐content characterization on the polished surface through the measurement on birefringence. The Boltzmann–Matano mathematical analysis was applied to the profile to obtain the Li2O‐content dependence of Li+ diffusivity. The results show that the diffusivity decreases with the decreased Li2O‐content and the decrease is by at least one order of magnitude as the Li2O‐content decreases by 1 mol% from 48.5 mol%. The diffusion shows slight anisotropy and is faster along the optical axis direction of crystal. In combination with previously reported result in the near‐stoichiometric regime, the diffusivity over the Li2O‐content range from 47 to 50 mol% is presented.