The present invention relates to a secondary cell and a method for supplementing an electrolyte of a secondary cell. The secondary cell according to the present invention comprises: an electrode assembly; a cell case for receiving an electrolyte in a receiving part formed therein; and a sealing member for further injecting the electrolyte, wherein the sealing member is formed in a part of the cellcase so as to supplement the electrolyte into the receiving part of the cell case by injection and allow the injected region to be sealed.