Radiation portal monitor (RPM) is an installed device to monitor illicit radioactive materials possibly embedded in loads at harbors.In Korea,RPMs have been installed at harbors in accordance with the Act on Protective Action Guidelines against Radiation in the Natural Environment which have enforced since July 26,2012.Nuclear Safety and Security Commission (NSSC),the regulatory body of Korea,has accomplished to install 10 RPMs in harbors,and have planned to increase a number of RPMs gradationally.However,according to the results from the investigations about suspicious materials (the loads which make radiation alarms from RPMs),most of them showed background radiation dose rate and the activity concentration under the exemption level pursuant to the Act,so it is necessary to reconsider the radiation alarm level.Moreover,some problems revealed to operate of RPMs and to take the actions for alarm-occurring cargos,so RPMs have difficulty fulfill their purpose what prevent the distribution of suspicious materials effectively.Therefore,the purpose of this research is to consider the points for operation optimization of RPMs by figuring out problems of current operation of RPMs in Korea.