Provided is a power control method in which a remaining battery time of a portable device can be ensured, and a portable device using the method. The power control method includes receiving externally a requested time-of-use and a type of one or more application programs to be executed; computing an estimated amount of power consumption when the application programs are executed for the requested time-of-use; measuring a remaining amount of power within the portable device; determining operation modes of elements of the portable device by using the estimated amount of power consumption and the remaining amount of power; and controlling operations of the elements according to the determined operation modes, in which the portable device allows a user to execute the application programs for the time-of-use requested by the user.