A transmission control system includes: a storage unit that stores therein zone identification information for identifying a zone in which each of transmission terminals is used, and priority information that indicates a priority at which a transmission terminal indicated by the zone identification information should use each of a plurality of relay devices, in association with each other; a reception unit that receives, from a first transmission terminal, first zone identification information for identifying a zone in which the first transmission terminal is used and second zone identification information for identifying a zone in which a second transmission terminal as a destination terminal is used; and a selection unit that selects a relay device to be used for relaying the content data based on first priority information associated with the first zone identification information and second priority information associated with the second zone identification information in the storage unit.