A communication device and a method for auto-locking an input interface thereof are provided. In the present invention, an external volume received by the communication device having the input interface is determined when the communication device enters a communication mode. Thereafter, the external volume is compared to a predetermined volume. An input function of the input interface is disabled if the external volume exceeds the predetermined volume. As a result, activation of other functions due to unintended touch of the input interface during a phone call can be avoided.