A layout structure of double-sided flexible circuit board includes a flexible substrate having a first surface and a second surface, a first circuit layer and a second circuit layer. An inner bonding region is defined on the first surface and an inner supporting region is defined on the second surface according to the inner bonding region. The first circuit layer is located on the first surface and includes first conductive lines which each includes an inner lead located on the inner bonding region. The second circuit layer is located on the second surface and includes second conductive lines which each includes an inner supporting segment located on the inner supporting region. A width difference between any two of the inner supporting segment of the second conductive lines is less than 8 μm.