Microindentation of the proton exchange layers on X cut of lithium niobate single crystals was performed. The results were interpreted in the framework of the proportional specimen resistance model. It was found that proton exchange causes increase in the load-independent ("true") hardness and decrease in the crystal elasticity. The elastic properties of proton exchange layers improve due to annealing while their load-independent hardness decreases. However, in all annealing conditions both hardness and elasticity cannot restore to the corresponding original values of the virgin lithium niobate. (C) 2012 Elsevier B.V. All rights reserved.