We present a facile and efficient fabrication of 3D macroporous rGO/MnO2 nanosheet thin-films for supercapacitor electrodes. An amorphous-carbon-modified rGO thin-film is firstly prepared through a simple glucose and CaCO3 particle mediated template method. Then ultrathin MnO2 nanosheets are in situ synthesized on the rGO networks by the rapid and scalable redox reaction between KMnO4 and amorphous carbon. The fabricated three-dimensional porous hybrid thin-film shows a high specific capacitance of 245 F g-1 (based on the total mass of the film) at a scan rate of 2 mV s-1, a good rate capability of 143 F g-1 at 300 mV s-1, and an excellent cycling stability, maintaining 81% of the initial capacitance after 2000 cycles at 2 A g-1. The improved performance indicates that the lightweight and low-cost 3D porous rGO/MnO2 nanosheet thin-films have a great potential in the area of portable energy storage devices.