Diffusion characteristics of Zr4+ in LiNbO3 single-crystal were studied. Zr4+-doped LiNbO3 crystal plates were prepared by in-diffusion of 100 nm thick ZrO2 film coated onto Z-cut congruent substrates in wet O2 at different temperatures. Zr4+-diffused profile was analyzed by secondary ion mass spectrometry. The results show that the Zr4+ diffusion follows the traditional diffusion theory. From the measured profiles, important diffusion parameters are obtained, such as diffusivity and its temperature dependence, diffusion constant, activation energy, surface concentration, and solubility. The Zr4+ has a diffusivity similar to that of Ti4+, implying that the Zr4+ doping and the Ti4+ diffusion can be performed simultaneously to simplify the fabrication process of a photorefractive-damage-resistant Zr4+-doped Ti-diffused LiNbO3 waveguide.