Disclosed is a cover for a foldable electronic device. The cover includes: a first cover portion configured to be coupled to a first housing of the electronic device, a second cover portion configured to be coupled to a second housing of the electronic device, a connecting portion provided between the first cover portion and the second cover portion and extending in a first direction, the connecting portion being configured such that the first cover portion and the second cover portion are folded to be superimposed on each other or are unfolded, and a pen holder configured to at least partially accommodate a pen and mounted on the connecting portion to be detachable.