A mobile communication system for providing carrier aggregation between digital units, and a method for processing a signal in the system are provided.The mobile communication system includes: a plurality of digital units connected to a core system and configured to process a radio digital signal; a blade server connected to at least two or more digital units and configured to perform resource allocation on signals processed by the connected digital units; and a plurality of radio units physically separated from the digital units, configured to convert and amplify digital signals received from the digital units, and transmit the same to a terminal, and configured to receive a signal transmitted from the terminal and transmit the received signal to the digital units. In the system, a mobile communication service is provided to the terminal by using carrier aggregation between radio units respectively connected to at least two or more digital units and using different frequencies.