A portable electronic device including a front cover, a back cover and a circuit board is provided. The circuit board is located between the front cover and the back cover. The back cover is combined with the front cover and includes a back section, a plurality of side sections and a separator, at least one of the side sections adjacent to the back cover includes a groove close to the back section and a slot far away from the back section, the slot is connected through to the groove, a first antenna unit and a second antenna unit are defined at the side section by the groove and the slot. The separator is located in the groove and the slot.