A chip on film package including a chip and a flexible film. The chip includes bumps disposed on the chip and is mounted on the flexible film. The flexible film includes first vias, second vias, upper leads and lower leads. The first vias and the second vias penetrate the flexible film and are arranged on two opposite sides of a reference line respectively. A distance between one of the first vias and one of the second vias, which are closer to a first side of the chip, is longer than that between another one of the first vias and another one of the second, which are further from the first side. The upper leads are disposed on the upper surface connected between the vias and the bumps. The lower leads are disposed on the lower surface and connected to the vias.