A portable cooling device has a vacuum bottle, a pump, an outflow pipe, a thermal exchanger and a return pipe. The vacuum bottle holds a coolant and has an outer casing and a vacuum flask. The outer casing has a chamber. The vacuum flask is mounted in the chamber. The pump is mounted on the vacuum bottle to pump the coolant out of the vacuum bottle. The outflow pipe connects to the pump. The thermal exchanger connects to the outflow pipe, is filled by the coolant and is placed adjacent to a person to lower his body temperature. The return pipe connects between the thermal exchanger and the vacuum bottle to form a flow circle. Consequently, the portable cooling device efficiently cools the body temperature. Moreover, having the vacuum bottle to hold and insulate the coolant elongates effective cooling time of the cooling device.