The experimental conditions for {111} twin formation in BaTiO3 mere investigated, When BaTiO3 compacts without excess TiO2 were sintered either in an oxidizing atmosphere lair) or in a reducing atmosphere (95N(2)-5H(2) no {111} twins formed within the BaTiO3 grains and no abnormal grain growth occurred. In contrast, many {111} twins were present within the abnormally grown grains in the eseess-TiO2-containing BaTiO3 samples sintered in air, while no twins were observed in the excess-TiO2-containing samples sintered in 95N(2)-5H(2). X-ray diffraction analysis showed that excess TiO2 forms a Ba6Ti17O40 phase during sintering with the space group A2/a in air and a Ba6Ti17O40-x phase with the space group C in 95N(2)-5H(2). It appears therefore that excess TiO2 and an oxidizing atmosphere are necessary for (111) twin formation in BaTiO3. These results may also indicate that the interface structure between BaTiO3 and Ba6Ti17O40 influences the twin formation.