Component effects such as a cocation and the zeolite support structure and the preparation condition effect of metal-loaded zeolites for the catalytic activity of direct NO, decomposition were examined using an experimental method. Regarding the cocation effect, the theoretical calculations were performed using a density functional method. The experimental results indicated that ZSM-5 was the best support of all of the zeolite tested such as ZSM-5, ZSM-11, SAPO-5, Y, and MOR, It was also experimentally found that the addition of a cocation such as Ca or Ni to Cu ion-exchanged ZSM-5 zeolite (Cu/ZSM-5) could prevent the catalyst from deactivation caused by O-2 or H2O in the reaction gas. Regarding the cocation effect of Ca or Ni on Cu/ZSM-5, the theoretical calculations showed that the addition of these cocations increased the catalytic activity by promoting the desorption of oxygen yielded from NO decomposition and maintained NO adsorption on the catalyst under the coexistence of H2O, These results of the calculations supported the experimental results.