A wearable electronic device includes a device body, a wearable body, a circuit board, an antenna system and a conductive extension portion. The device body includes an upper casing and a lower casing. A feeding portion, a first grounding portion and a second grounding portion are disposed on a periphery of the circuit board. The second grounding portion is electrically connected to the upper casing. The antenna system is disposed on the inner surface of the lower casing. The feeding terminal of the antenna system is electrically connected to the feeding portion of the circuit board. The grounding terminal of the antenna system is electrically connected to the first grounding portion of the circuit board. An end of the conductive extension portion is electrically connected to the upper casing, the other end of the conductive extension portion is extended into the wearable body.