New dinuclear methoxo-bridged manganese(III) complex [Mn2((MeO-bph)en)2Cl2(m-CH3O)2] (1) was synthesized by template reaction of 2-hydroxy-4-methoxybenzophenone, 1,2-ethanediamine and MnCl2×6H2O with molar ration (1:1:1) in methanol as solvent. The title compound 1 was characterized by elemental analyses (CHN), Fourier Transform infrared spectroscopy (FT-IR) and single crystal X-ray diffraction. X-ray result reveal that 1 is dimeric with methoxo bridges between two symmetry equivalent manganese ions. The Mn ions are surrounded in a distorted octahedral geometry influenced by Jahn-Teller effect. The tridentate Schiff base ligand MeO-bp-en and one of the methoxo-bridges bind in the equatorial mode, whereas in the axial positions, other metoxo-bridge and Cl atom bind to the Mn ions. Thermogravimetric analysis of 1 was studied and display the title compound 1 decompose in three stages. Finally, by calcination of 1 at 500 °C for 3 h, we prepared Mn2O3 particles and characterized by FT-IR, XRD and SEM.