Electrochemical reaction process of iron oxide reduction has been investigated for several decades, and both solid-state reaction mechanism and dissolution/re-deposition mechanism were proposed for the reduction process. The previous studies observed the reaction process from macro-and micro-scale, and how the intermediate participates in the dissolution/re-deposition route is unclear. In this study, a mixture of Fe2O3 nano-particles and carbon powder was electrolyzed in an alkaline solution, and the morphology of the product depended on the electrolysis temperature. The Fe2O3 nano-particle aggregates can be electrolyzed into micro-size hollow partciles at 60 degrees C. To explain this phenomenon, ex-situ SEM technique combining with TEM was adopted to observe the morphology change of Fe2O3 particles on the surface of the glass carbon electrode at nano-scale at a series of electrode potentials. The surface of the particle was reduced to amorphous compounds firstly, and these compound was the intermediate participating in dissolution/re-deposition process to form new crystals. The solubility of these amorphous compound is relative low at 60 degrees C, and the compouds stayed in their original position, connected and stabilized each other to form micro-size iron shell. They can dissolve into eletrolyte, migrate to somewhere, and re-deposit to construct new crystals at higher temperature. This study not only presents an innovative and efficient way to electrolyze micro-size hollow iron particles, but also provides some new discovery about Fe2O3 electrochemical reduction process. (c) 2017 The Electrochemical Society. All rights reserved.