An external sound box includes a connecting member and a sound box. The connecting member includes a sound passage and is selectively attachable to a surface of an electronic device to cover a sounding hole of the electronic device. The sound box is mounted to the connecting member. The sound box defines a resonant chamber communicating with the sound passage and a sounding output hole. Sound generated by the electronic device moves from the sounding hole into the sound passage and the sound box. The sounding passage and the sound box are configured so that the sound from the sounding hole resonates before exiting the sound output hole with increased volume.