A multi-cyclone dust-collecting apparatus for a vacuum cleaner mounted in a main cleaner body to separate dust from air flowing from a suction port body and collect the dust separated from the air, the apparatus including a dust-separating unit including a primary cyclone unit to separate large dust particles contained in the air flowing from the suction port body, and a secondary cyclone unit that is disposed inside the primary cyclone unit and that tapers downwards; and a dust-collecting unit detachably mounted in a lower portion of the dust-separating unit, the dust-collecting unit including a first dust-collecting chamber to collect the large dust particles discharged from the primary cyclone unit, and a second dust-collecting chamber disposed inside the first dust-collecting chamber to collect fine dust particles discharged from the secondary cyclone unit. The first dust-collecting chamber may be greater in volume than the second dust-collecting chamber.