Filtered containment venting system (FCVS) removes radioactive iodine and cesium released from the reactor vessel during the severe accident. The silver doped zeolite (AgX) which is a promising sorbent for CH_3I can remove over 99.99% of CH_3I in the vent gas. However, the evidential experiment data of CH_3I sorption on AgX is quite limited. In this study, therefore, labeled CH_3I by ^<125>I was synthesized by isotope exchange reaction, and it was devoted for sorption experiment on AgX. Sorption experiment using stable CH_3I was also examined by the same method. After the sorption experiment, Color of AgX samples changed to yellow and formation of Agl in AgX was confirmed by XRD analysis. For evaluation of the apparent sorption capacity of AgX, CH_3I was continuously injected until breaking through AgX. The result indicated that the apparent sorption capacity for CH_3I was 0.25g / g (AgX) at 24℃.