The invention relates to a battery management system to estimate a state of charge of a battery and a driving method thereof includes a sensing unit and a micro control unit. The sensing unit measures a battery voltage. The MCU measures a first time and a second time, detects first and second battery voltages that respectively correspond to the first and second times from the battery voltage, estimates an open circuit voltage by the first and second voltages, and establishes the SOC that corresponds to the OCV.