A mobile terminal and power source controlling method thereof are disclosed, by which power consumption can be efficiently controlled in a low power mode. The present invention includes calculating a remaining power level of a power supply unit, if the calculated remaining power level is equal to or lower than a predetermined reference, entering a power saving mode, if the power saving mode is entered, activating a basic operation related module, if the power saving mode is entered, comparing a power consumption level required for a designated operation execution to the calculated remaining power level, and if the remaining power level is equal to or higher by a predetermined level or more than the power consumption level as a result of the comparing step, outputting designated operation execution possibility indication information.