Provided are a method for performing handover in a cellular mobile communication system that supports a carrier aggregation, and a user equipment and a node base (NodeB) using the method. A connection between the user equipment and the NodeB may be maintained and information may be exchanged using a plurality of serving carriers. Before performing the handover, the user equipment may perform measurement with respect to a neighboring NodeB supporting the carrier aggregation, and may provide parameter information to the NodeB in order to support a carrier aggregation function required for the handover. In a handover seamless environment, the continuity of a service may be provided and the performance of the service may be enhanced.