A flexible printed circuit comprising a substrate, a plurality of function lines, and a plurality of first dummy lines. The substrate comprises at least two periphery areas and an intermediate area. Each periphery area comprises a first layout region, a second layout region and a first rough region disposed between the first and second layout regions. The intermediate area is disposed between the periphery areas. The function lines are disposed on the substrate and within the intermediate area. The first dummy lines are disposed on the substrate and within the first or second layout area.