The present invention relates to a method in which a mobile node having mobility performs handover in a mobile communication system, and more particularly, to a fast handover method and system using network-based localized mobility management. According to an exemplary embodiment of the present invention, in a network access process between a mobile node and a base station, the base station sends a message allowing network access to the mobile node and a link-up message to an access router. Then, the access router sends a location registration message, which includes a mobile node identifier, a target base station identifier, a localized mobility anchor identifier, and access permission flag information, to a localized mobility anchor (LMA), and receives an acknowledgement (Ack) message including network prefix information. Accordingly, when a router advertisement (RA) message is sent to the base station, the mobile node performs duplicate address detection (DAD). Accordingly, fast handover is performed to reduce packet loss and delay that occur when the mobile node moves between networks, thereby minimizing the packet loss and delay.