Abstract: In a method for operating a power source of a mobile communication terminal, when a user selects a module, the mobile communication terminal allows the user to be informed in advance whether the corresponding function can be executed or not by comparing the total consumption current for operating the corresponding module with a supply of available current and notifies the user whether or not the selected module can be operated. By notifying the user in advance whether the selected module can be operated or not, the terminal can be prevented from being suddenly turned off and the power source can be effectively used.