Multirod and hierarchically spherical 3D Co1-xMnxO (2/3 <= x <= 1) nanostructures have been successfully synthesized by the decomposition of acetylacetonate precursors. Their morphologies could be controlled through tuning the heat rating which affects the nucleation. The rods grew along [ 110] directions to reduce the appearance of high-energy crystallographic {110} planes. The hierarchically spherical superstructures were formed by a three-dimensional oriented-attachment mechanism. Magnetic measurement indicates that the MnO nanomaterials with hierarchically spherical superstructures show an antiferromagnetic transition temperature at 121 K, similar to that of bulk, and a ferromagnetic ordering exists at low temperature. Such anomalous magnetic properties arise plausibly from their microstructure characteristics.