LiNbO3 precursor gels with a variety of molecular structures were prepared by the sol-gel method by changing the amount of added water and other conditions of synthesis. The molecular structures, as well as the thermal behaviour of the amorphous precursors, were studied by Raman spectroscopic analysis and differential thermal analysis-thermogravimetry in order to determine the influence of the structures on the resulting LiNbO3 formation. The crystallization to LiNbO3 by the combustion heat of the residual unhydrolysed alkyls was observed at similar to 300 degrees C for the homogeneous precursors prepared from a double alkoxide (LiNb(OC2H5)(6)) without added water, but the LiNbO3 formed had low crystallinity. When using the hydrolysed double alkoxide, the synthesized precursors transformed to LiNbO3 at similar to 480 degrees C after the structural relaxation. This temperature can be assigned to the real crystallization point. Indeed the unhydrolysed double alkoxide is necessary to prepare the high-quality LiNbO3 films, and heat treatment above similar to 500 degrees C is required to obtain good crystallinity. Even for the inhomogeneous precursors prepared from LiOC2H5 and NbO(C2H5)(5), lithium ion diffusion and the structural relaxation occur, to form the uniform molecular structures from 300-400 degrees C.