The concept of the photonic bandgap(PBG) is extended to a novel architecture wh ich consists of two fractal PBG plates stacked up in the direction perpendicular to the plane of the substrate. This novel, dual-layer fractal PBG is presented here as the substrate for a microstrip line, and the resulting configuration builds a low-pass filter of wide stop-band. In the specific design, the dual-layer PBG includes two kinds of fractal PBGs with different periodicities in which one fractal PBG consists of a first-order Sierpinski carpet, and the other consists of third-order Sierpinski gasket. Simulated and measured transmission parameters in comparison with the corresponding two filters with monolayer PBG show that the filter with the proposed fractal PBG drastically enhances the width of the stop-band.