The amount of traffic in the data center grows exponentially due to the emergence of many resource-starvation applications. Thus, effective resource allocation in the data center becomes vitally important. In this letter, the tenants’ resource demands are abstracted as Virtual Data Center (VDC) requests and fulfilled by mapping virtual nodes and links of VDC onto physical servers and fiber links. Software Defined Networking (SDN) is leveraged to build a multi-tenant oriented resource allocation framework, in which the resource allocation problem is transformed to a VDC mapping problem crossing different domains, and a cost and security aware mechanism is proposed to address this problem. The results indicate that the proposed mechanism can effectively increase the resource utilization and cut down the probability of servers being attacked.