Cloud computing, featured by shared servers and location independent services, has been widely adopted by various businesses to increase computing efficiency, and reduce operational costs. Despite significant benefits and interests, enterprises have a hard time to decide whether or not to migrate thousands of servers into the cloud because of various reasons such as lack of holistic migration (planning) tools, concerns on data security and cloud vendor lock-in. In particular, cloud security has become the major concern for decision makers, due to the nature weakness of virtualization - the fact that the cloud allows multiple users to share resources through Internet-facing interfaces can be easily taken advantage of by hackers. Therefore, setting up a secure environment for resource migration becomes the top priority for both enterprises and cloud providers. To achieve the goal of security, security policies such as firewalls and access control have been widely adopted, leading to significant cost as additional resources need to employed. In this paper, we address the challenge of the security-aware virtual server migration, and propose a migration strategy that minimizes the migration cost while promising the security needs of enterprises. We prove that the proposed security-aware cost minimization problem is NP hard and our solution can achieve an approximate factor of2. We perform an extensive simulation study to evaluate the performance of the proposed solution under various settings. Our simulation results demonstrate that our approach can save 53%moving cost for a single enterprise case, and 66% for multiple enterprises case comparing to a random migration strategy.