A power headroom report method and apparatus of a User Equipment (UE) provides an efficient resource allocation in a mobile communication system. The power headroom report method of the present disclosure includes calculating a power headroom change by comparing the current power headroom and the previous power headroom. The method also includes determining, when the power headroom change is greater than a predetermined threshold value, whether a report prohibit timer set to a predetermined value has expired. The method further includes reporting the current power headroom when the report prohibit timer has expired, and resetting the prohibit timer to a different value.