We introduce TeaVisor, which provides bandwidth isolation guarantee for software-defined networking (SDN)-based network virtualization (NV). SDN-NV provides topology and address virtualization while allowing flexible resource provisioning, control, and monitoring of virtual networks. However, to the best of our knowledge, the bandwidth isolation guarantee, which is essential for providing stable and reliable throughput on network services, is missing in SDN-NV. Without bandwidth isolation guarantee, tenants suffer degraded service quality and significant revenue loss. In fact, we find that the existing studies on bandwidth isolation guarantees are insufficient for SDN-NV. With SDN-NV, routing is performed by tenants, and existing studies have not addressed the overloaded link problem. To solve this problem, TeaVisor designs three components: path virtualization, bandwidth reservation, and path establishment, which utilize multipath routing. With these, TeaVisor achieves the bandwidth isolation guarantee while preserving the routing of the tenants. In addition, TeaVisor guarantees the minimum and maximum amounts of bandwidth simultaneously. We fully implement TeaVisor, and the comprehensive evaluation results show that near-zero error rates on achieving the bandwidth isolation guarantee. We also present an overhead analysis of control traffic and memory consumption.