A mobile communication device includes a control circuit unit, a first interface, a status change detecting circuit, and an embedded controller. The control circuit unit is operated in either a normal working mode or a power-saving mode. The first interface is connected with the data card and the control circuit unit. The status change detecting circuit is connected with the first interface. The embedded controller is connected with the status change detecting circuit and the control circuit unit. If the control circuit unit is operated in the power-saving mode and the data card is switched from a standby status to a working status, the data card generates a status-changing signal to the status change detecting circuit. In response to the status-changing signal, the control circuit unit is controlled to be switched from the power-saving mode to the normal working mode by the embedded controller.