A method and battery management system performing cell balancing for a battery pack includes measuring a voltage of each of a plurality of battery cells in a battery pack, selecting one of the plurality of battery cells as a battery cell subject to cell balancing based on the measured voltages, selecting one of a plurality of resistors as a resistor on which cell balancing is performed, and outputting the voltage of the battery cell subject to cell balancing from a multiplexer that receives the voltage of each of the plurality of battery cells to the resistor on which cell balancing is performed.