A slot antenna structure for an electronic tag includes a dielectric layer, a conductor layer, a slot area and a capacitance adjustment unit. The electronic tag includes an identification chip. The conductor layer is disposed on the dielectric layer. The slot area is disposed in the conductor layer and includes an open slot, an open end and at least one closed slot. The open end is located at an edge of the conductor layer and extends inwardly to form the open slot for disposing the identification chip. The open slot has two sidewalls, and the two sidewalls have at least one turning point at a bottom portion of the open slot to form the closed slot. The capacitance adjustment unit is disposed on a surface of the dielectric layer different from the conductor layer to correspond to the slot area, thereby generating a capacitance effect.