Barium titanate ultra-fine particles prepared by sol–gel (SG) and stearic acid-gel (SAG) methods are studied by high-resolution transmission electron microscopy (HRTEM). Physical property measurements showed that the barium titanate particles made by the SAG method are quite different from those particles prepared from sol–gels and from normal barium titanate ceramics and crystals (Ren et al., Chin. Phys. Lett. 11(5) (1994) 310). SAG barium titanate fine particles contain a high density of defect structures such as multiple-twins and intergrowth structures containing hexagonal BaTiO 3. Image processing of the HRTEM images also showed a high density of small defects for the SAG barium titanate fine particles and ceramics. The defect density was much lower and no such defects were observed for SG barium titanate. The unusual ferroelectric properties of SAG barium titanate particles and ceramics are discussed in terms of the observed defect structures.