Transient behavior of local liquid-holdup of air-kerosene fluids in periodically operated trickle-bed reactor (TBR) is investigated in an acrylic column (140mm ID and a height of 980mm) packed with 3.6mm glass spheres using a nonintrusive technique of electrical capacitance tomography (ECT). Local liquid-holdups determined from ECT images of normalized permittivity are experimentally calibrated under the steady-state operation with that from the classic drainage method. The instantaneous ECT images are captured at several axial positions along the column for the periodically operated TBR with slow-mode. The effect of periodic operation parameters (split, period, and time-average flow rate) on the instantaneous profiles of local liquid-holdup is firstly examined compared with the previous results. Transient variations of radial distributions of liquid and their maldistribution factor are calculated and further analyzed to provide more liquid distribution information under periodic operations. (C) 2009 Elsevier Ltd. All rights reserved.