In the next-generation networks, guaranteeing QoS is one of the important factors, which allows QoS supportable networks such as UMTS and 802.16e to be deployed together. Under such networks, a mobile node (MN) with multiple interfaces demands for the QoS service continuity during a handover. The 802.21 framework enables MNs to freely move in multiple networks. However, supporting QoS service continuity remains as a problem to be solved. In this paper, we propose a network-initiated handover based on the 802.21 framework to provide the QoS service continuity in UMTS/802.16e networks. To support the QoS service continuity, we design a detailed handover procedure that consists of three steps; QoS measurement, passive reservation, and activation. Through our performance evaluation, we show that the proposed handover scheme provides the QoS service continuity of MNs during a handover in terms of guaranteed data rates and latency.