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The microstructural characteristics of a highly conductive Nb-doped SrTiO3 thin film grown on (0 0 1) SrTi03 substrate by laser molecular beam epitaxy were extensively studied by means of transmission electron microscopy. It was found that the film was of single-crystal form and epitaxially grown on the SrTi03 substrate forming a flat and distinct interface. Threading dislocations were hardly found within the film and their absence is believed to be the main contributor to the good electrical properties. The Nb-riched nano-agglomerates, which are homogeneously embedded in the film, were found to induce the diffusion interfaces with their surrounding mediums. Pure edge misfit dislocations with Burgers vectors of a<0 1 1> type and line directions of <1 0 0> were found to be the major interfacial defects responsible for the misfit relief. Such dislocations were further dissociated into two equal partial dislocations with Burgers vectors of a/2<0 1 1>. The high conductivity of the film was discussed from the viewpoint of Nb dopant and the lower oxygen pressure. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.