A roaming service method in a mobile broadcasting system and a system thereof are provided. A terminal receives a service guide from a corresponding visited service provider (Visited SP) when the terminal moves to a roaming area. The terminal transmits a roaming request message for requesting a purchase item allowable for individual services to a home service provider (Home SP) based on the received service guide. Upon receipt of the roaming request message, the Home SP negotiates roaming availability and allowable scope for each individual service with the Visited SP where the terminal is located, based on the roaming request message. The Home SP transmits the roaming availability and allowable scope for the individual service, negotiated with the Visited SP, to the terminal.