Experiments were conducted in a small cyclone separator (50 mm inner diameter) with two grades of commercial polyethylene particles, to study the electrostatic charge generation during the transportation and separation. Results show clearly that the charges generated in the cyclone test unit were quite reproducible. When solid particles were fed to the cyclone, there was an abrupt change in the current flow and a quick increase of (negative) charge generation for both types of polyethylene particles. Both the charge density and the charge generation rate were always higher for the particles of higher density and smaller mean size. For both types of polyethylene, the (negative) charge density increased almost linearly with the gas velocity. When the solid feed rate or initial solid loading increased, the magnitude of the charge density decreased because there were fewer particle-wall collisions at higher solids feeding rate or higher solids concentration, due to shielding effects. Results indicate that the pipe section contributed < 10% of the total charge generation for both grades of polyethylene, with charge generation being dominated by the interaction between the particles and the cyclone internal surface.