The effect of NiO and pseudoboehmite content in raw materials on the performances of spray-dried oxygen carriers was investigated. Oxygen carriers were prepared by the spray-drying method using 60, 70, and 80 wt % NiO and γ-Al2O3. For 70 wt % NiO, γ-Al2O3 mixed with 0, 5, and 10 wt % pseudoboehmite was used as raw support materials. The prepared oxygen carriers showed excellent physical properties suitable for fluidized-bed process applications. Oxygen carriers prepared using 70 wt % NiO showed higher attrition resistance than that of other oxygen carriers and a commercial fluid catalytic cracking catalyst. Especially, the calcination temperature to obtain sufficient mechanical strength was lowered to 1000 °C for the oxygen carrier prepared using 70 wt % NiO and 30 wt % γ-Al2O3. The oxygen carriers prepared using 70 and 80 wt % NiO and calcined at 1100 °C showed high oxygen transfer capacities and oxygen utilization above 13.3 wt % and 88.7%, respectively. However, the oxygen utilization of the oxygen car...