Oxygen carrier materials in chemical looping applications exhibit physical and chemical variations during cyclic oxidation-reduction exposure at elevated temperature, which often lead to material degradation. While ideal chemical reactions of pure components may be predicted thermodynamically, structural changes of materials in chemical looping systems are complex and continuous due to the redox nature of the process. In this work, structural variations in two types of oxygen carrier particles (alumina-supported Cu/Fe spinel and natural hematite) during repeated redox exposures at 800°C were investigated in situ using a customized heat chamber attached to a confocal scanning laser microscope. Volume changes of the micron particles corresponding to each exposure cycle were recorded real time. Volume changes along with other structural degradation influence oxygen accessibility into the particles; impacting the oxygen exchange capability of a material. Structural degradation will be discussed based on a lattice structure changes, void formation in inner grains and particles, diffusion of the constituents, and sintering/densification with different structures.