A method is provided for performing, by a user equipment (UE), a power headroom reporting (PHR) procedure in a wireless communication system. In a first PHR procedure, a first PHR is triggered, and it is determined that a first uplink (UL) resource cannot accommodate a PHR media access control (MAC) control element (CE) plus its subheader. The PHR MAC CE is not transmitted in the first PHR procedure and it is determined that the first PHR is not cancelled. Further, in a second PHR procedure, a second PHR is triggered, and it is determined that at least one PHR, including the first PHR and the second PHR, has been triggered and not cancelled. It is then determined that a second UL resource can accommodate a PHR MAC CE plus its subheader, and the PHR MAC CE is transmitted by using the second UL resource to an eNodeB (eNB).