Effect of the hydrothermal treatment was studied for [110]-oriented BaTiO3 ceramics. It was found that the hydrothermal treatment increased the degree of the [110] orientation F110 of [110]-oriented BaTiO3 ceramics with reduced grain size. As the autoclave temperature increased, the F110 and d33 increased. A large piezoelectric response of d33=517 pC/N was observed for the BaTiO3 ceramic with a small grain size of 1.76 µm and F110 of 85.3%.