In this paper results of Particle Image Velocimetry (PIV) measurements of the particle flow velocity fields in a wire.-to-plate type electrostatic precipitator (ESP) are presented. One or two grounded stainless-steel plate electrodes and seven wire electrodes in the middle of the ESP height were used. The measurements were carried out in the plane placed perpendicularly to the wire electrodes (for the ESP version with two plate electrodes) and in four planes placed parallel to the wire electrodes (for the ESP version with one plate electrode). Either negative or positive voltage polarity was applied to the wire electrodes. The main gas flow velocity was 0.14 m/s. The obtained results showed strong influence of the electrohydrodynamic (EHD) forces on the How patterns, which exhibited strong upstream and downstream vortexes. The experiment confirmed that the flow patterns in the ESP have 3-dimensional character.