A power brush assembly for vacuum cleaners is disclosed. In the power brush assembly, a casing is set in the suction part of a vacuum cleaner and defines a suction nozzle used for sucking dust-laden air under pressure into the suction part of the vacuum cleaner. A power brush is set within the casing such that the brush is rotatable and reciprocable to the left and right. This power brush is used for brushing dust and impurities on a target surface. A drive motor generates a rotating force for allowing the power brush to rotate and reciprocate to the left and right within the casing. A power transmission mechanism connects the drive motor to the power brush so as to transmit the rotating force of the drive motor to the power brush. In this power brush assembly, the brush body of the power brush performs a linear reciprocating action in addition to a rotating action, and so the brush assembly effectively and actively brushes a target surface at areas corresponding to the gaps between opposite ends of the brush body and opposite sidewalls of the casing. This brush assembly thus improves the dust cleaning effect of a vacuum cleaner.