A rack-mounted server system includes a rack, a number of server units mounted in the rack adjacent to a front end of the rack, a fan module, and a number of power units located beside the server units. The rack includes a back wall defining an air outlet aligned with the server units. The fan module is fixed to the back wall and fitted in the air outlet. The power units are arranged in front of the fan module. An air-guide plate is mounted in the rack between the fan module and the power units to guide a part of the airflow generated by the fan module to flow through the power units.