Highly epitaxial La0.5Ba0.5CoO3 (LBCO) thin films with sharp interface and a thickness of 200 nm were epitaxially grown on (001) SrTiO3 substrates using pulsed laser deposition. High-resolution transmission electron microscopy and electron diffraction analysis revealed that the films have a triple-layered structure. The first layer, close to the film/substrate interface, has a thickness of similar to 6 nm and is a defect free single crystal disordered cubic structure (a = 3.882 angstrom) which has a lattice mismatch of - 0.59% with respect to the substrate. The second layer which dominates the film structure has a single crystal disordered cubic structure (a = 3.854 angstrom) which has a lattice mismatch of - 1.31% with respect to the substrate. The third layer located on the top of the film has a thickness of several nanometers and consists of 112-type ordered tetragonal structure. The cubic structures in the first and second layer have an orientation relationship of (001)(LBCO)//(001)(STO) and < 100 >(LBCO)//< 100 >(STO) with respect to the substrate. Self-patterned 3-dimensional nano structures with a dimension range from 2 to 10 nm were formed in the second and third layers. These nano structures were formed by the enclosure of anti-phase boundary planes which are parallel to the {100} of the cubic structure. Epitaxial LBCO thin films with such nano structures are hard ferromagnetic with a large coercive field value and magnetoresistance effect value (similar to 24%), and exhibit semiconductor behavior at temperatures <300 K. (c) 2011 Elsevier B.V. All rights reserved.