Removal of gaseous radioactive iodine (I-131 and I-129) compounds from nuclear facilities is an important issue. Herein we assessed the adsorptive capacity of gaseous non-radioactive methyl iodide ((CH3I)-I-127) as a simulant on two commercial TEDA-metal impregnated activated carbon(AC)s. The characterizations of the ACs were determined ICP-MS, XPS, and 77 K N-2 isotherms. As a result, it was found that one AC has a small amount of TEDA but a well-developed porosity, and the other one was abundant with TEDA, but the porosity was relatively less developed. The methyl iodide removal performances were evaluated under 10 ppm and 400 ppm using breakthrough experiments under various relative humidities (RH). Desorption was also carried out using nitrogen after adsorption to investigate adsorption affinity. Methyl iodide adsorption capacity of TEDA-rich AC decreased significantly as RH increased at 10 ppm. Conversely, performance degradation was clearly observed from less TEDA-impregnated AC with well-developed porosity as RH increased at 400 ppm. It is demonstrated that the amount of physisorbed methyl iodide is decreased as RH increased. Although moisture decreases the adsorption amount, it enhances the adsorption affinity. Also, additional TEDA impregnation to ACs results in improving the performance under severe condition (RH90%, 400 ppm).