A vacuum sealing cap for a container includes an outer cap body, an inner cap body movable toward or away from the outer cap body, a sealing gasket compressible by the outer cap body to abut sealingly against the mouth of the container when the inner cap body moves toward the outer cap body, a slide member connected to the inner cap body, and an operating member connected pivotally to the slide member and pivotable between first and second positions, where the operating member pulls upwardly and pushes downwardly the slide member to move the inner cap body upwardly toward and downwardly away from the outer cap body. The sealing gasket is pressed and is not pressed sealingly against the mouth of the container in the first and second positions, respectively.