A mobile device includes a metal back cover, a ground metal element, a feeding radiation element, and a dielectric substrate. The metal back cover has a slot. The feeding radiation element has a feeding point, and includes a first feeding branch, a second feeding branch, and a third feeding branch. The second feeding branch and the first feeding branch extend in opposite directions. The third feeding branch and the first feeding branch extend in the same direction. The feeding radiation element has a vertical projection on the metal back cover, and the vertical projection at least partially overlaps the slot. The dielectric substrate is disposed adjacent to the metal back cover. The ground metal element and the feeding radiation element are disposed on the dielectric substrate. An antenna structure is formed by the feeding radiation element and the slot of the metal back cover.