The exposed crystal facets of the catalysts are crucial to the catalytic performances for soot combustion as a typical heterogeneous catalysis reaction. Herein, we have successfully synthesized the well-defined catalysts of alpha-Mn2O3 nanocrystals with three morphologies of octahedrons (alpha-Mn2O3-O), truncated octahedral bipyramids (alpha-Mn2O3-TOB) and hexagonal nanosheets (alpha-Mn2O3-HN) via the adjusting amount of glucose in the hydrothermal method, and their predominantly exposed facets are {111}, {211} and {001}, respectively. The catalytic activities of alpha-Mn2O3 catalysts for soot combustion were tuned by the exposed crystal facet of alpha-Mn2O3 arranged in the order: alpha-Mn2O3-HN > alpha-Mn2O3-TOB > alpha-Mn2O3-O, and the alpha-Mn2O3-HN catalyst shows the highest catalytic activity during soot combustion, its T-10, T-50 and T-90 values are 282, 373 and 424 degrees C, respectively. The alpha-Mn2O3 catalysts possess good catalytic stability during four cycles of soot-TPO. The crystal facet-dependent activity of alpha-Mn2O3 catalysts for soot combustion is systematically investigated by means of various characterizations. The exposed {001} crystal facets of alpha-Mn2O3-HN catalyst can improve the surface density of active oxygen species and enhance the low-temperature reducibility of Mn4+ species. The research highlights a new strategy to the fabrication of efficient alpha-Mn2O3-based catalysts for the catalytic removal of diesel soot particles or other pollution.