A portable electronic device includes an expansion base module, a hinge mechanism mounted slidably on the expansion base module and slidable relative to the expansion base module, a docking unit pivoted to the hinge mechanism, defining a docking groove, and including a docking connector, and a system module including a panel having two opposite sides that respectively have two opposing end portions inserted into and detachably retained in the docking groove. The system module further includes a system connector that is mounted on the panel and that mates with the docking connector.