An electrostatic precipitator having a rotor supported for rotation within a housing containing inlet and outlet openings adjacent the opposite ends thereof. The rotor is formed by a plurality of ringlike collector plates which are fixedly connected in axially spaced relationship. One end of the rotor, as disposed adjacent the outlet opening, is closed by a support plate. The collector plates are alternately of opposite charge to create electrostatic fields therebetween. The collector plates have aligned central openings which decrease in diameter towards the closed end of the rotor. The plates also have equal surface areas so that substantially equal electrostatic fields are created between each adjacent pair of plates. The collector plates, in the radially outward direction, are sloped in a direction which is axially opposite to the direction of the gas supplied to the inlet opening. An ionizing device is disposed across the inlet opening to the rotor for ionizing the foreign particles entrained in the gas supplied thereto. The ionizing device includes a plurality of ionizing wires disposed perpendicular to the rotational axis of the rotor, which wires are uniformly spaced between grounded flow divider bars which also extend perpendicularly of the inlet opening.