Provided are a method in which a source base station (BS) transmits a Quality of Service (QoS) flow-to-data radio bearer (DRB) mapping rule to a target BS in a wireless communication system, and a device supporting the same. The method may include: receiving, from a user equipment (UE), a measurement result of a target cell; determining the handover of the UE to the target BS on the basis of the measurement result; and transmitting, to the target BS, a handover request message including a QoS flow-to-DRB mapping rule of the source BS.