This paper reports on two topics regarding nanosized barium titanate (BaTiO₃) prepared by the sol–gel method using a highly concentrated alkoxides precursor solution. One topic concerns the crystallographic features of the BaTiO₃ nanoparticles. In the case of using a highly concentrated precursor solution, non-core–shell BaTiO₃ nanocrystals with a small amount of intraparticle voids, lattice hydroxyl groups and remaining alkoxy groups were efficiently generated by the addition of less excess water during aging at room temperature. The generation of the high-quality BaTiO₃ nanocrystals is considered to be due to the hydrolysis and polycondensation reaction of the alkoxides being well promoted in such a concentrated solution. The lattice volume of the BaTiO₃ nanocrystals with a crystallite size of 15 nm fired at 600°C was approximately 1 vol % larger than that of bulk crystal. This lattice expansion is more likely to be caused by an intrinsic size effect than an extrinsic effect due to the lattice defects, such as lattice hydroxyl groups. The other topic concerns the dielectric properties of dense nanograin free-standing films with a grain size of 57 nm after applying the same sol–gel method. Significant frequency dispersion behavior of dissipation factor was observed at temperatures less than the Curie temperature. This finding may indicate that the dielectric properties reflect an intrinsic grain size effect without any influence being attributed to the film/substrate interface or lattice defects.