The present invention relates to an uplink synchronization request method in a mobile communication system, a CDMA allocation information element structure thereof, and an apparatus using the same. For this purpose the uplink synchronization request method includes: when uplink traffic is generated, determining whether an uplink synchronization error occurs; when the uplink synchronization error occurs, calculating a timing adjustment value; and transmitting a bandwidth request code including the calculated timing adjustment value to a base station and performing a bandwidth request. According to the present invention, the PSS compares a reference adjustment value and an arrival time of a downlink preamble to calculate uplink synchronization timing and synchronize an uplink of the PSS that requests bandwidth allocation through a bandwidth request ranging process to thereby maximize resource use efficiency in the uplink synchronization.