A support unit comprising a cover, a positioning unit and a bracket is provided. The cover is pivotably connected to a housing of the portable electronic device and can be received in the housing. The positioning unit is fixed to the housing and includes a plurality of limiting recesses. The bracket includes a first end and a second end that opposite. The first end is connected to the positioning unit, and the second end is pivotably connected to the cover. When the cover is expanded out of the housing, the first end of the bracket is driven by the cover to move relative to the positioning unit, and then the first end of the bracket is engaged with a limiting recess of the positioning unit to fix the expansion angle of the cover relative to the housing. A portable electronic device including the support unit is also provided.