A back cover structure disposed on the back of the portable electronic device includes a cover body, a plurality of replaceable adornments and a switching structure. The cover body has an outer surface, an inner surface opposite to the outer surface and facing the portable electronic device, and a through hole passing through the cover body and connected between the outer surface and the inner surface. The replaceable adornments are applied to the cover body, and any one of the replaceable adornments is adapted to and detachably disposed in the through hole of the cover body according to different requirements. The switching structure is disposed on the inner surface of the cover body to secure the replaceable adornment on the cover body or release the replaceable adornment from the cover body.