We studied the material characteristics of polycrystalline films of lithiumniobate (LiNbO₃) and its components (Li₂O and Nb₂O₅) prepared by Low Pressure Metal Organic Chemical Vapor Deposition (LPMOCVD). Precursors are Li(DPM) and Nb(DPM)₂Cl₃, and the carrier gas is nitrogen or argon with 50% of oxygen at 5 Torr. We proposed a quantitative model far Nb₂O5 film growth. Li₂O film grows on alumina substrate under argon+oxygen atmosphere, but Li₂CO₃ grows under nitrogen+oxygen atmosphere. On silicon or silica substrate, both react to form lithium silicates. By feeding both precursors, we found the optimum condition for preparing LiNbO₃ film from a film composition map as a function of the reaction temperature vs Li mol % in feed gas.