A method and apparatus for updating firmware of terminals in a mobile broadcast system including a Broadcast Service Distribution/Adaptation fragment (BSDA) and a Broadcast service Subscription Management (BSM). The method includes requesting creation of a content fragment, by the BSM, by transmitting a firmware package file for a firmware update of the terminals to the BSDA; creating a content fragment including the firmware package file and broadcasting the created content fragment to the terminals by the BSDA; detecting the firmware package file from the received content fragment; and performing the firmware update using the firmware package file.