The spinel Fe3O4 powders were synthesized using 0.2 M-FeSO4·7H2O and 0.5 M-NaOH by oxidation in air and the spinel LiMn2O4 powders were synthesized at 480 ℃ for 12 h in air by a sol-gel method using manganese acetate and lithium hydroxide as starting materials. The synthesized LiMn2O4 powders were mixed at portion of 5, 10, 15 and 20 wt% of Fe3O4 powders using a ball-mill. The mixed catalysts were dried at room temperature for 24 hrs. The mixed catalysts were reduced by hydrogen gas at 350 ℃ for 2 h. The carbon dioxide decomposition rates of the mixed catalysts were 90% in all the mixed catalysts but the decomposition rate of carbon dioxide was increased with adding LiMn2O4 powders to Fe3O4 powders.