A method for producing a non-aqueous electrolyte secondary battery according to the present invention is characterized in that the method comprises the steps of: placing an electrode body into an outer casing, the electrode body having a folded-separator structure or a wound structure in which a positive electrode including a positive-electrode active material and a negative electrode including a negative-electrode active material are stacked with a separator interposed therebetween; placing a non-aqueous electrolyte free of a flame retardant into the outer casing; charging the electrode body by applying a voltage between the positive electrode and the negative electrode placed in the outer casing; placing a flame retardant into the outer casing; and sealing the outer casing, wherein the step of charging is a step of charging the electrode body with the state in which the surface of the positive-electrode active material and the surface of the negative-electrode active material are in contact with the non-aqueous electrolyte substantially free of the flame retardant.