Influences of iron precipitation on particle cohesiveness related to agglomeration and defluidization in Fe2O3 reduction were investigated in a visual fluidized bed reactor. A new method of the controlled defluidization tests was employed to examine the evolution of bed agglomeration. The real-time agglomeration tendency was represented by the defluidization temperature. Results showed that defluidization potential increased by increasing metallization degree. According to thermo-mechanical analysis, the precipitation of metallic iron significantly reduced the sintering temperature and surface viscosity of Fe2O3 particles, resulting in the evolution of the bed materials from cohesiveless to sticky. The SEM analysis showed that fine iron nuclei with nano/micro size on the surface acted as necks to form agglomerates by sintering and enhanced particle cohesiveness. Thus, the metallized bed particles tended to adhere and resulted in bed defluidization. The calculated adhesive force between particles depended on both metallic iron content and surface viscosity, which was in good agreement with the experiment results for defluidization. (C) 2014 Elsevier B.V. All rights reserved.