In this study, a group of submicro BaTiO3 ceramics ranging from 330 nm to 1.05 μm was successfully prepared by a two-step sintering process and the dependence of electric and mechanical properties on grain size was investigated. By dynamic mechanical analysis (DMA), phase transitions and grain size effects on modulus and internal friction were clearly detected. A clear low-frequency relaxation behavior induced by Debye relaxation was characterized in orthorhombic phase for fine BT ceramics. Furthermore, Arrhenius relationship was applied to theoretically analyze the relaxation peak, for which 90° domain wall motion was considered to be responsible. Another anomaly peak around 70 °C became more obvious after annealing in oxygen atmosphere, which was caused by the surface charge release, the interaction between domain walls and stress, and size effect.