Vertical handover apparatus and method in a wireless communication system are provided. The method includes examining whether there exists an accessible target network while communicating with a serving network; when there exists the accessible target network, linking up to the target network; changing a communication state to an idle mode by de-registering the linked target network; and performing a network re-entry to the target network in a vertical handover to the target network. When the terminal can execute the vertical handover without the seamless service support and reduce the handover delay.