Because of the popularity of WLAN, UMTS and WLAN networks are often combined into two-tier heterogeneous networks. However, it is important for mobile hosts to have an end-to-end QoS support for service continuity in the UMTS/WLAN interworking systems. To maintain mobility in the QoS control of multimedia services when integrating UMTS and WLAN networks, an efficient resource management mechanism for the two-tier network is necessary. This paper proposes a heterogeneous RSVP extension mechanism, denoted as HeMRSVP (Heterogeneous Mobile RSVP), which allows mobile hosts to reach the required QoS service continuity while roaming across UMTS and WLAN networks. A performance comparison of HeMRSVP and conceivable two-tier resource management schemes is presented. Besides, two approaches were studied, namely hierarchical reservations as well as repacking on demand, for the performance enhancement of HeMRSVP. Numerical results show that the HeMRSVP significantly outperforms other two-tier resource management schemes and the enhanced mechanisms perform well in UMTS/WLAN combination networks.