Disclosed is a dust collector of a vacuum cleaner. The dust collector comprises: a cyclone body forming a cyclone chamber and having a bottom wall and an air inlet, air being admitted into the cyclone chamber and rotating in the cyclone chamber; an outlet pipe extending upwardly from the bottom wall of the cyclone body; and a dust-bin body surrounding the cyclone body in such a manner that a dust collection space is formed between the dust-bin body and the cyclone body. The inner diameter of the cyclone body is increased as approaching a height near the top end of the outlet pipe from the bottom wall of the cyclone body.