Wi-Fi Direct technology enriches local services that enables social interactions off the grid. Allowing purely local connections among mobile devices, Device-to-Device (D2D) networks support more versatile proximity-based applications and reduce dependence on central entity. While the D2D paradigm allows more convenient information exchanging or resource sharing, it also brought new challenges. Information assurance and system security are top concerns users have. In this paper, we studied the impacts of Denial-of-Service (DoS) attacks in a D2D underlaying network. Our experimental results show that malicious users can effectively force the victim mobile device drop off its Wi-Fi connection to the access point (AP) without being detected by the AP or the cellular network. We expect this preliminary results can inspire more research in this raising area.