An ultra-thin flexible electronic device of the invention, comprises: a flexible printed circuit board (FPC), having a circuit layout arranged thereon; an input element, electrical-connected to the FPC for setting up a data; a display, electrical-connected to the FPC for displaying the data; a power supply, connected to the FPC for providing electricity to the FPC, the input element and the display through the circuit layout; a thin substrate, being disposed to lay over the FPC and the power supply; and a polymer film; wherein the FPC, the input element, the display, the power supply and the thin substrate are all flexible.