A communication system for supporting carrier aggregation and a method and apparatus for updating system information thereof are disclosed. A method for providing system information in the communication system supporting carrier aggregation includes: when system information of said communication system changes, generating first information including information for indicating the change of system information; determining a first cell of a terminal related to the change of system information, wherein said first cell is one of cells to which said terminal connects, and corresponds to a carrier unit currently used by said terminal for keeping connection with a base station of said communication system; and transmitting said first information to said terminal through said first cell.