This study examines the effects of manganese (Mn) on zeolite-supported Ni catalysts for dry reforming of methane (DRM). Three commercially-available zeolites (NH4-ZSM5, NH4-Y, Na-Y) were used as catalyst supports for the Ni (10 wt%) catalysts, and 4 different loadings of Mn (0-15 wt%) were used. The activities of the catalysts were screened, and selected catalysts were investigated for 24 hours in the DRM reaction. It was found that the effects of Mn on catalyst activity depends upon the type of zeolite support. Generally, however, Mn decreased the activity of the zeolite-supported Ni-based catalyst, but reactivity was more stable over a 24 -h reaction period. The beneficial effects of Mn as a promoter on NH4-ZSM5 and NH4-Y zeolites are to reduce carbon deposition, to decrease the crystal size of Ni, and to increase Ni dispersion on the zeolite. However, as Mn loading increases, the crystallinity of the zeolite structure and its micropore surface area generally decrease. Mn loading at 10 wt% and 15 wt% on Na-Y is detrimental to catalyst activity and to crystal structure, as it facilitates the destruction of the crystal structure of the Na-Y zeolite and significantly enhances sintering in a high temperature reducing atmosphere.