This paper reports that OH^- absorption bands of lithium niobate crystal have been measured at room temperature, and the band shape depending on the crystal composition has been observed. The OH^- absorption bands are fitted with three Lorentzian peaks by varying position, halfwidth, and height. Nearly constant peak positions （3468, 3481 and 3490 cm^-1） are obtained for all samples. It shows that the height and area of the decomposed peaks vary with the Li composition in a complex way. However, the combinations of these fitting parameters show a linear dependence on the composition up to nearly 50 mol%, which is very useful for the composition determination in a wide range. The linear relationships between the parameter combinations and Li composition are also presented quantitatively. In addition, the explanations were given for the excellent composition linearity of parameter combinations.
