An antenna device includes a supporting body and an antenna. The supporting body has two arms and a connecting portion disposed between and connecting the two arms. The antenna has a grounding portion extending from one end of one of the arms. A free end of the grounding portion perpendicularly extends toward the other arm to form a first radiating strip, and a second radiating strip, a third radiating strip and a fourth radiating strip are respectively integrally formed in turn. The first, second, third and fourth radiating strips together define substantially a rectangular shape. A feed-in portion extends from the first radiating strip. The grounding portion connects the supporting body functioning as a ground of the antenna, which increases the area of the grounding for the antenna and enhances the performance of signal transmitting and receiving of the antenna device.