An apparatus and method for battery state of charge (SOC) estimation can reduce the estimation error in the battery SOC. The apparatus includes a charge/discharge current detection unit, a terminal voltage detection unit, a first estimation unit that estimates a first SOC by integrating the charge/discharge current value, a second estimation unit that estimates an open circuit voltage value from the charge/discharge current value and the terminal voltage value and estimates a second SOC from the open circuit voltage value, a first difference calculation unit that calculates a SOC difference between the first SOC and the second SOC, an error estimation unit that estimates, based on the SOC difference, an error as a state quantity of an error model by using the error model, and a second difference calculation unit that calculates a SOC of the battery by subtracting the error from the first SOC.