Filtered containment venting system (FCVS) is an emergency response system for severe accident. FCVS reduces the pressure in reactor vessel and removes radioactive iodine and cesium. Recently, silver doped zeolite (AgX) has been attracting attentions since it is believed to remove over 99.99% of CH3I in the ventilation gas. However, the reliable data of AgX for CH3I sorption under expected severe accident conditions are still limited. Therefore, the sorption behavior of CH3I on AgX was investigated under several expected conditions. In this study, the CH3I labeled by 125I tracer was synthesized by isotope exchange reaction, and it was devoted for sorption experiment on AgX. Sorption experiment using stable CH3I was also conducted by the same procedure. From results of the sorption experiment, over 99.9% of 2.28g of CH3I were sorbed by 10g of AgX. After the sorption experiment, AgX samples were analyzed by powder X-ray diffraction (XRD) and SEM-EDX. These results indicated the distribution of Ag agreed with that of I in micro area of AgX. For the evaluation of apparent sorption capacity of AgX, breaking through experiment was carried out. The apparent sorption capacity of AgX for CH3I was determined as 0.25g / g (AgX) at 24°C. The breaking through experiment was also carried out for the evaluation of CH3I flux and humidity effects in the vent gas. The effect of temperature on the sorption capacity was also studied. When the flux of CH3I supply was increased from 1.09×10-4 to 2.33 × 10-4g/cm2s, apparent sorption capacity was unchanged (=0.21g / g (AgX)). Besides, the apparent sorption capacity was unchanged in the humidity range of ∼0 % H2O to 0.01 % H2O, while it decreased to 0.19 g / g (AgX) at 3% H2O. When sorption temperature increased to 170°C, the apparent sorption capacity also increased to 0.69 g / g (AgX).