A method and apparatus are provided for transmitting power headroom information by a terminal in a mobile communication system. The method includes receiving, by the terminal, information for an allocated uplink transmission resource; identifying whether a path loss has changed by more than a threshold, after transmitting last power headroom information, when the terminal has the allocated uplink transmission resource; in case that the path loss has changed by more than the threshold when the terminal has the allocated uplink transmission resource, determining a transmission of the power headroom information; and transmitting an uplink packet including the power headroom information based on the allocated uplink transmission resource. The power headroom information is obtained based on a difference between a maximum transmission power of the terminal and a transmission power of the terminal.