Grain-aligned polycrystalline lithium titanogallate, Li0.91Ti0.48Ga4.40O8 (LTGO), was successfully prepared by the combined techniques of reactive diffusion and ion exchange. We firstly synthesized the b-axis-oriented polycrystal of sodium titanogallate (NTGO) by the reactive diffusion between NaGaO2 and Ga2TiO5 at 1323 K for 24 h, followed by the ion-exchange reaction of Li+ for Na+ at 773 K for 125 h. The crystal structure of resulting LTGO (space group C2/m) was isomorphous with that of the original NTGO. Both crystal structures were built up of five types of polyhedra; [MO7] (M = Li or Na), [(Ti,Ga)O6], [Ga1O6], [Ga2AO4], and [Ga2BO6]. There was a marked difference between the two structures for the coordination environment of M; the centroid-to-M distance of [LiO7] (0.026 nm) was significantly larger than that of [NaO7] (0.008 nm). The lithium-ion conductivity along the b-axis steadily increased from 3.41 × 10− 4 to 6.21 × 10− 4 S cm− 1 with increasing temperature from 773 to 1073 K. The activation energy of conduction was 0.22 eV. The combination of the two distinct techniques would enable us to synthesize the grain-aligned polycrystalline materials with various constituent compounds and chemical compositions.