Molten hydrated salt was used, for the first time, as a new kind of solvent to explore the synthesis of complex oxide nanomaterials. Employing Ba(OH)23 8H2O as the solvent, and rutile TiO2 as the reactant, core-shell and hollow nanoparticles of perovskite-type BaTiO3 were successfully fabricated under sealed conditions at 180 C. No other additive was introduced into the reaction system. The effect of various reaction conditions on the morphology and size of the products was investigated. At high TiO2 dosage, core-shell BaTiO3 particles were the dominant products with their sizes between 400 and 800 nm, whereas relatively low TiO2 dosage favored the formation of hollow BaTiO3 particles less than 250 nm. The formation process of the products was investigated, and can be attributed to an Ostwald ripening induced hollowing mechanism. Because of its simplicity and scalability, the molten hydrated salt method may open up a promising route for the synthesis of complex oxide micro/nanomaterials for practical applications.