A new kind of medium material is developed for chemical-looping combustion, in which fuel is oxidized by metallic oxide medium in a reactor and reduced metal is oxidized by air in another reactor. This scheme may yield great advantage of savings of energy and suppressing the effect on environment, Two kinds of methods, sol-gel method and dissolution method, are examined to prepare the particle of NiO mixed with YSZ (i.e., yttria-stabilized zirconia) as an excellent medium material from the viewpoint of chemical kinetics and mechanical strength, The effects of reaction temperature, particle size, and gas composition are clarified experimentally. The experimental results on kinetics are interpreted by unreacted-core shrinking model, The cyclic use of the medium particle is also tested, The results obtained in this paper disclose the high potentiality that the chemical-looping combustion could be applied in a practical power plant.