A Chip on Film (COF) flexible circuit board and a display device using the COF flexible circuit board are provided. The circuit board includes: a substrate; a plurality of conductive terminals arranged separately in parallel over the substrate, each of the plurality of conductive terminals including a wide line and a narrow line; and a anisotropic conductive adhesive region provided over the substrate. A connection site of the wide line and the narrow line is located in an overlapping area of the anisotropic conductive adhesive region and the substrate. The embodiments of the invention can reduce the probability of the circuit board being broken and the undesirable phenomena such as open circuit.