A heat dissipation device includes a first casing, a second casing, a thin pump, and a cooling member. The second casing is connected to the first casing to form a first accommodating space and a second accommodating space adjacent to and communicating with the first accommodating space. The thin pump is disposed in the first accommodating space. The cooling member is disposed in the second accommodating space and has a plurality of spacers, and the spacers and the thin pump are disposed on the same plane of the first casing. A portable electronic device having the heat dissipation device is also disclosed.