An antenna structure includes an antenna portion having an antenna defining a feeding point and a grounding point, and a grounding portion electrically connecting with the grounding point of the antenna. The grounding portion defines a basic board. The basic board is bent upwardly from edges thereof to form a first extending portion. The first extending portion is bent inwardly from a top edge thereof to form a second extending portion approximately paralleling with the basic board. Through the first and second extending portions, the area of the grounding portion is extended. And the electric field is widely distributed all over the whole grounding portion including the basic board and the first and second extending portions to decrease the SAR of the antenna.