The present invention relates to a multi-cyclone dust collector for a vacuum cleaner and dust collecting chamber. The multi-cyclone dust collector includes a first cyclone unit having a first cyclone body and a first dust collecting chamber, the first cyclone body taking dust-laden air entering through an under portion thereof and forming a first upwardly whirling air current so as to separate contaminants centrifugally from the dust-laden air, the first dust collecting chamber collecting contaminants discharged from the first cyclone body; and a second cyclone unit wrapping around at least a portion of the first dust collecting chamber, sucking semi-clean air discharged from the first cyclone unit through an under portion thereof, taking the sucked semi-clean air and forming a second upwardly whirling air current so as to separate contaminants centrifugally from the semi-clean air.