A mixture of titanium dioxide and an oxide or carbonate of barium includes one or more transition metal elements selected from the group of V, Cr, Mn, Fe, Co, Ni and Cu, in the amount of 2 ppm or more. This mixture is used as a starting material. The mixture is heated to a predetermined temperature to make a melt. Then, a seed crystal of BaTiO.sub.3 is brought into contact with the melt under an environment with a low oxygen partial pressure of 0.02 atm. or less. From this state, the above melt is slowly cooled to grow a single crystal on the seed crystal. The thus obtained single crystal is heated in a temperature of 600 .degree. C. or more, under an oxidizing environment with its oxygen partial pressure more than 0.1 atm.