An antenna structure includes a dielectric substrate, a ground plane, and a main radiation element. The main radiation element and the ground plane are disposed on two opposite surfaces of the dielectric substrate. The main radiation element has a first loop-shaped slot and a second loop-shaped slot. The first loop-shaped slot is inside the second loop-shaped slot. The first loop-shaped slot includes a first slot, a second slot, a third slot, a fourth slot, a pair of first partition slots, a pair of second partition slots, a pair of third partition slots, and a pair of fourth partition slots. The first slot, the second slot, the third slot, and the fourth slot are interleaved with the first partition slots, the second partition slots, the third partition slots, and the fourth partition slots.