The ultrafine Mn-Zn ferrite (MnO)_0.37 (ZnO)_0.10(Fe₂O₃)_0.53 has been prepared by the amorphous citrate process. Extra pure manganese metal (99. 95%), zinc metal(>99. 99%) and iron metal (>99. 99%) are dissolved into 6N HNO₃ to prepare stoichiometric aqueous solution of manganese nitrate, zinc nitrate and ferric nitrate. Nitrate salts are avoided as starting materials, since they are strongly hygroscopic in nature. The nitrate solution is mixed with citric acid and ethylene glycol in a uniform solution. The water and nitric oxides are evaporated at around 90°C and ethylene glycol is dried at aruond 120°C to yield a solid precursor material. The precursor is fired to high temperature to form the desired compound. The decomposition mechanism is studied with thermogravimetric analysis, differential thermal analysis and X-ray diffraction. Also, magnetic properties and BET surface areas are measured for heat-treated powders.