A heat-dissipating assembly includes a body and a bottom plate. The body has a heat-absorbing portion. The interior of the heat-absorbing portion is provided with a chamber covered by the bottom plate. The chamber has an evaporating region for generating a high pressure, and a condensing region for generating a low pressure. The pressure gradient between the evaporating region and the condensing region is used to drive the circulation of liquid/vapor phase of a working fluid. With this structure, heat can be conducted rapidly without providing any wick structure.