A method for making a heat dissipating device includes the steps of: mounting an elastically deformable member on a container body in such a manner that the elastically deformable member covers a periphery of an opening in the container body and that the elastically deformable member cooperates with the container body to define a cavity in fluid communication with an inner space in the container body through the opening; vacuuming the inner space in such a manner that air in the inner space is drawn through the opening and the cavity to the outside of the container body; filling the inner space with a predetermined amount of a working fluid through the opening and the cavity; and forming a sealing mechanism that functions to isolate the inner space from the opening.