Engineered domain configuration was induced into barium titanate (BaTiO3) single crystals, and the d33 piezoelectricity was investigated as a function of domain size. Prior to the domain engineering, the dependence of domain configuration on the temperature and the electric-field was investigated, and above Curie temperature (Tc), when the electric-field over 16 kV/cm was applied along c direction, the fine engineered domain configuration appeared. On the basis of the above information, the 33 resonators with different domain sizes were successfully prepared. Their piezoelectric measurement revealed that the d33 of the 33 resonators with fine-engineered domain configurations were higher than those of BaTiO3 single-domain crystals. Moreover, d33 increased with decreasing domain sizes. The highest d33 of 289 pC/N was obtained in the BaTiO3 crystal with a domain size of 13μm.