Disclosed is a method for estimating a state of charge (SOC) of a secondary battery using a full charge capacity (FCC) of the battery, the method including (S1) measuring voltage and current of the battery, (S2) calculating the FCC using a voltage change and a current integral of the battery during a specific time, (S3) estimating a time remaining until the battery is fully discharged using the calculated FCC and the measured voltage and current to calculate a self-discharge rate, (S4) calculating a capacity deterioration rate of each charge cycle of the battery, and (S5) applying the calculated self-discharge rate and the calculated capacity deterioration rate to estimate the SOC of the battery.