An apparatus for allocating resources in a communication system includes a reception unit configured to receive information on a terminal from the terminal when the terminal initially accesses the apparatus in order to receive communication service, a determination unit configured to check information on a bandwidth for providing the communication service to the terminal, the information on the terminal, and information on a satellite and determine the size of a resource block group to be allocated to the terminal by taking the information on the bandwidth, the information on the terminal, and information on the satellite into consideration, and an allocation unit configured to allocate resource blocks corresponding to the size of the resource block group to the terminal in order to transmit and receive data packets to and from the terminal.