The structure of the Li1-xTi2-xInxP3O12 solid solution system was investigated by means of the P-31 MAS NMR technique. The results indicate that In 3+ ions can substitute for Ti4+ ions in the lattice of LiTi2P3O12 and a series of homogeneous solid solutions without amorphous and other phosphate phases is formed. The five basic structure units Q0(4-yTi, yIn) (y = 1, 2, 3, 4) of the compound are predicated from the resulting P-31 NMR spectra. The resonant frequencies for those structures can be determined by a linear correlation between the P-31 isotropic chemical shift and the field strength of the cations.