A chip on film package includes a base film, a patterned circuit layer, a chip and a reinforcing sheet. The base film includes a first surface, a second surface opposite to the first surface and a mounting region located on the first surface. The patterned circuit layer is disposed on the first surface. The chip is mounted on the mounting region and electrically connected to the patterned circuit layer. The reinforcing sheet is disposed on the first surface and/or the second surface and exposes the chip, wherein a flexibility of the reinforcing sheet is substantially equal to or greater than a flexibility of the base film.