A double-sided flexible circuit board includes a flexible substrate, a first circuit layer, a second circuit layer, an insulating protection layer and a plurality of through circuit lines. The first and second circuit layers are located on a top surface and a bottom surface of the flexible substrate, respectively. The insulating protection layer covers a supporting line of the second circuit layer such that the supporting line is located between the flexible substrate and the insulating protection layer. The insulating protection layer can provide electrical insulation to the supporting line of the second circuit layer to avoid short circuit conditions of the double-sided flexible circuit board during test.