Methods and apparatus are provided for reporting a Power Headroom (PH) of a User Equipment (UE) in a wireless communication system having a plurality of aggregated uplink carriers. A method includes receiving a configuration message to configure at least one uplink carrier; triggering a power headroom report (PHR) for a first uplink carrier if a predetermined event occurs; detecting an allocation of an uplink transmission resource for the PHR; identifying whether the first uplink carrier for which a power headroom (PH) is to be determined is different from a second carrier to which the uplink transmission resource is allocated; determining the PH based on a first pathloss associated with the first uplink carrier, if the first uplink carrier is different from the second carrier; and transmitting the PHR generated based the determined PH.