A protective case assembly includes a detachable component having a component outer peripheral surface, a casing body having at least one casing body protrusion, and a coupling unit detachably coupling the detachable component to the casing body and including at least one first protrusion extending outwardly from the component outer peripheral surface, at least one second protrusion extending outwardly from one of the at least one first protrusion and the component cuter peripheral surface and cooperating with the at least one first protrusion to define therebetween an engaging groove for engaging with the at least one casing body protrusion, and at least one main groove formed in the casing body for receiving the at least one second protrusion.