NiO/Al2O3, known as one of the most efficient oxygen carrier, has been fabricated by spray-drying method and calcinated at 1100 °C and 1300°C, and the structural characteristics are investigated using XRD, SEM, TEM and XPS. For the characterization of surface and bulk microstructure of the fabricated NiO/Al2O3 oxygen carrier particle, investigated were 1) as-fabricated powders, 2) internal structure of the crumbled particles, and 3) cross-sectional specimens. The results showed that the fabricated oxygen carrier formed well distributed NiAl2O4 with NiO particles of 100~500 nm via reaction keeping on the mole ratio. The oxygen carriers developed in this study showed pertinent characteristics for chemical-looping combustion, and good effect on the strength, indicating a potential for wide application in the future. The calcination at 1100 °C was good enough and as efficient as that at 1300 °C.