A wearable electronic device assembly includes: a wearable electronic device having a speaker therein; and a case configured to accommodate the wearable electronic device. The wearable electronic device includes: a housing having the speaker therein; and a microphone spaced apart from the speaker inside the housing. The case includes: a lower body defining a space therein for accommodating the housing; an upper body rotatably coupled to the lower body; and a protrusion portion protruding outwardly from the lower body or the upper body and is configured to be seated on the protrusion while the upper body is in a closed state with respect to the lower body.