Wireless headphones having a built-in flexible battery are provided. Wireless headphones having a built-in flexible battery according to an exemplary embodiment of the present invention comprise: a band part having at least one fastening portion; a pair of headset parts, each of which includes a speaker unit for receiving a wirelessly transmitted audio signal and outputting the audio signal to the outside, and is connected to the band part; and a plate-shaped flexible battery which is embedded in the band part so as to supply power to the headset parts, and has a to-be-fastened portion corresponding to the fastening portion so as to be fixed in position when coupled to the band part.