Abstract: The single-phase nano-particles of MnO, Mn₃O₄, and Mn₂O₃ in similar sizes and different morphologies were prepared by low-temperature combustion synthesis method through controlling the mole ratio of organic fuel (carbamide) and nitrate (manganese nitrate).Scanning electron microscopy shows that, the sizes of these three nanoparticles are about 100 nm in the morphologies as chain-like, potato-like, and ball-like, depending on the valence of Mn ions.The thermogravimetric–differential thermal analysis indicates that, the particle size is essentially determined by the ignition temperature of fuel.The magnetization measurements show that, the MnO and Mn₂O₃ nano-particles exhibit a weak ferromagnetic behavior at low temperature, which can be attributed to the presence of uncompensated spins on the surface of nanoparticles.This paper offers an environmental friendly and industrially steadily method to prepare the high-purity manganese oxide nano-particles in different Mn valence states.