Nanometer size ferroelectric domains, having a width as small as one unit cell, are observed in ultra-thin BaTiO 3 films (2–10 nm thick) using high resolution TEM. Only 180° domains and 90° domain boundaries are formed in nano-multi-domains structures. Most of the domains are oriented in-parallel to the film plane. The film is under tensile stress, which increases to about 8.7 GPa with decreasing the film thickness to 2 nm. The BaTiO 3 films exhibit a ferroelectric behavior characterized by a polarization hysteresis loop, two transition temperatures, switching and fatigue. The switching response is in the range of few nanoseconds and follows a one dimensional growth kinetics. Fatigue tests show an initial degradation of the remanent polarization after 10 7 cycles, which is comparable to bulk-size BaTiO 3 domains.