1H nuclear magnetic resonance measurements in proton‐exchanged LiNbO3were employed to determine structural positions of sites believed to be responsible for the desirable optical properties of this material. Contributions from other proton sites were first subtracted from the line shape which was subsequently analyzed by Van Vleck’s second moment method using a spin‐echo technique to separate like‐spin from unlike‐spin contributions. Among various models examined, only one in which protons are located on oxygen planes nearest to normal lithium sites, midway between two oxygen anions in an oxygen triangle, was found to be consistent with the data. ©1995 American Institute of Physics.