A method for isolating a flexible substrate from a support substrate and method for fabricating a flexible electronic device are provided. The method for isolating a flexible substrate from a support substrate includes providing a flexible substrate with a bottom surface. A surface treatment is subjected to the bottom surface of the flexible substrate, forming a bottom surface with detachment characteristics. The flexible substrate is fixed on the support substrate by means of an adhesive layer, wherein the bottom surface with detachment characteristics faces the support substrate. The flexible substrate is cut and isolated from the support substrate.