To investigate the effects of porous properties of supports on the methane decomposition of Co-Mo/MgO catalysts, supports having different porous properties were prepared by varying the synthesis temperature of MgO. Co-Mo/MgO catalysts were prepared using the impregnation method. The CM/4MgO catalyst using 4MgO support, which had the largest specific surface area of 170 m2/g, showed highest methane conversion of 85.7 % with 60.12 % of MWCNT production. The produced MWCNT on CM/4MgO had highest crystallinity and electrical conductivity with average diameter of 20.5 ± 7.8 nm. Overall, the improved pore structure of MgO prepared by the oxidation process enhanced the dispersibility of the Co active metal, thereby improving methane conversion and MWCNT production.