A Subscriber Identification Module (SIM) card for a portable wireless terminal is provided. The SIM card includes a SIM contact pad group which is exposed to an outer surface of the SIM card, and is electrically connected when the SIM card is placed in the portable terminal so as to identify subscriber information; a battery cell which is embedded in the SIM card, and is electrically connected when the SIM card is placed in the portable terminal so as to be used as an auxiliary power source; and a battery contact pad group which is electrically connected to the battery cell and is exposed to the outer surface of the SIM card; and a mode change element which is disposed to a lateral side of the SIM card and by which either an auxiliary battery function or a SIM function is selected by a user's manipulation.