Provided is a method of preventing a Transmission Control Protocol (TCP)-based Denial of Service (DoS) attack on a mobile device. The method efficiently prevents a DoS attack on a mobile device, which wirelessly and constantly transmits TCP packets to the mobile device using a TCP protocol and thereby exhausts resources of a wireless network and also battery power of the mobile device depending on a battery. An attack conventionally made in a wired network by abusing TCP-based three-way handshaking is more severe in the wireless network of mobile devices. To prevent such an attack on a mobile device, the method capable of checking three-way handshaking and each transition operation makes the mobile device check whether or not a received TCP packet is valid. Therefore, it is possible to efficiently prevent a DoS attack from exhausting wireless resources and battery power of the mobile device.