A method of changing a serving Base Station (BS) in a mobile communication system, and a mobile communication system for implementing the method, are provided. The method includes setting a minimum UpLink (UL) quality value, receiving DownLink (DL) quality values for a current serving BS of a User Equipment (UE) and respective BSs included in an active set of the UE from the UE periodically based on a predefined first period, receiving UL quality values for the serving BS and the respective BSs included in the active set from the serving BS and the respective BSs included in the active set periodically based on a predefined second period, determining if the UL quality value for the serving BS is less than the minimum UL quality value, when, as a result of the determination, the UL quality value for the serving BS is less than the minimum UL quality value, selecting BSs, which have UL quality values equal to or greater than the minimum UL quality value among the BSs included in the active set, as candidate BSs, and determining a BS, which has a maximum DL quality value among the candidate BSs, as a new serving BS of the UE, wherein the active set represents a set of BSs that can provide DL/UL service to the UE.