The hydrolysis and crystallization of the surfaces of sol-gel derived lithium niobate precursor films were analyzed by XPS and XRD. The Nb/Li ratio was 1.3 in the surface composition of amorphous films and 1.2 in that of partially crystallized films. These findings showed that the ratio finally approaches to 1 that is the stoichiometric composition ratio, depending on the progress of the crystallization in the films. The preheat-treatment of the precursor films in humidity was effective for decreasing the crystallization temperature. This was due to the releasing of the acetic acid chelating the precursor molecules. In the process of analyzing the composition of the lithium niobate film surface, Li was selectively etched.