The purpose of root end filling material in endodontic surgery is to provide a seal to prevent the ingress and egress of bacterial toxins into the periapical area. One reason for the sealing ability of these materials is their expansion upon setting. The aim of this study was to compare the percent linear setting expansion of WMTA and ERRM putty fast set using a linear voltage displacement transducer (LVDT) under controlled temperature of 37° Celsius. Materials were prepared according to the manufacturer’s instructions and packed into the hollow hydrophilic porous tubing. Approximately 200 µL of HBSS was added to the porous tube in order to initiate the setting reaction. Expansion changes were measured until it appeared to have plateaued. ERRM putty showed a significantly greater mean percent expansion compared to the MTA (P≤0.005). MTA expanded an average of 0.109% (0.08%-0.20%) while ERRM putty expanded an average of 6.63% (2.93%-8.89%).