Wireless Local Area Networks (WLANs) are currently among the most important technologies for wireless access. In order to exploit their full potential, wireless networks need to be planned carefully. However, chaotic unplanned Access Point (AP) placement are becoming the norm rather than an exception and causing interference among APs in the real environment. Interferences among APs often decrease the throughput. In this paper, we propose Virtual AP (VAP) Aggregation which aggregates functions of APs. For VAP Aggregation, it is necessary to run functions of two or more APs on an AP and enable Mobile Nodes (MNs) to connect its belonging domain. We adopt virtualization techniques for the mechanism of APs. And we adopt virtual networks for communication. In addition, through implementing a prototype system, we confirmed that VAP Aggregation is efficient for improving throughput.