Compared to other manganese oxides, characterizations of gamma - Mn2O3 are rare for both nanoparticles and the bulk material. We produced gamma - Mn2O3 nanoparticles with particle diameters ranging from ID to 15 nm and investigated, for the first time, their magnetic properties. The X-ray diffraction pattern shows that gamma - Mn2O3 nanoparticles possess a tetragonal structure with lattice constants of a = 5.790 angstrom and c = 9.402 angstrom. We observed a coercivity as high as similar to 8000 Oe at 5 K and a phase transition from ferrimagnetic to paramagnetic at 39 K.