A method and a device for controlling external data network use via a mobile Access Point (AP) are provided. A host device set as the mobile AP determines whether a data-less mode is set, blocks a client device from using the external data network via the mobile AP, if the data-less mode is set, and permits the client device to use the external data network via the mobile AP, if the data-less mode is released. A client device connected to a mobile AP determines whether a data-less mode is set for a host device set as the mobile AP, if the client device is connected to the host device in a state of being connected to a wireless data network, maintains the connection to the wireless data network, if the data-less mode is set, and releases the connection to the wireless data network, if the data-less mode is released.