Proton exchange waveguides were fabricated by buffered acid (benzoic acid doped with a certain amount of lithium benzoate) in Z-cut LiNbO3. The effective diffusion coefficients and the index profile were calculated for the waveguides fabricated in buffered benzoic acid with different molar fractions of lithium benzoate with aspect to benzoic acid (0.5%, 1.0% and 1.5%). The effective diffusion coefficient decreases exponentially as the molar fraction of lithium benzoate increases. The surface index increment decreases linearly with the increase of the Li+ mole percent in the proton source. The stabilities of these fabricated waveguides are studied. The results are compared with those from the waveguides fabricated by pure benzoic acid. The stabilities of LiNbO3 proton exchange waveguides can be improved by the exchange with buffered benzoic acid.