A mobile device includes a metal mechanism element, a dielectric substrate, and a feeding radiation element. The metal mechanism element has an open slot. The open slot substantially has an L-shape. The dielectric substrate is adjacent to the metal mechanism element. The feeding radiation element has a feeding point. The feeding radiation element is disposed on the dielectric substrate. The feeding radiation element at least partially extends along the open slot. An antenna structure is formed by the feeding radiation element and the open slot of the metal mechanism element. The antenna structure covers a first frequency band, a second frequency band, and a third frequency band.