With two-dimensional particle image velocimetry (2D-PIV), planar flows can be well examined when there is no out-of-plane (perpendicular to the lightsheet plane) flow motion. In gas cyclones, the turbulent swirling flows are three-dimensional. When they are investigated by 2D-PIV, contamination is introduced into the experimental results due to the existence of considerable out-of-plane velocity caused by the tangential gas motion. In this paper, an experimental method is introduced to investigate the axial and radial velocities by 2D-PIV, followed by the proposed contamination-removing schemes. The contamination on the axial velocity has been efficiently eliminated whereas that on the radial velocity is difficult to evaluate. The radial velocity distribution is then obtained based on a local mass balance calculation. The flow pattern in the dust hopper is also well examined.