A method and apparatus for receiving a power headroom (PH) report by a base station in a mobile communication system supporting carrier aggregation are provided. The method includes receiving an extended PH report (PHR) including respective PHs for multiple activated serving cells and respective indicators corresponding to the respective PHs through one of the multiple serving cells, and checking each indicator to determine whether a corresponding PH is calculated based on a real transmission or a reference format. It is determined that the corresponding PH is calculated based on the real transmission, if the each indicator is set to “0”, and it is determined that the corresponding PH is calculated based on the reference format, if the each indicator is set to “1”.