Provided is a method of activating a secondary battery, which includes an operation of deriving a reduction reaction voltage according to an electrolyte additive, a pre-charging operation of pre-charging the secondary battery into which an electrolyte containing the electrolyte additive is injected, and a pre-aging operation of wetting an electrode assembly accommodated in the secondary battery with the injected electrolyte and aging the electrode assembly, wherein a charging termination voltage in the pre-charging operation is less than the reduction reaction voltage.