In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general attains static charges arising from particle-wall collisions in the initial periods of conveying process and then reaches equilibrium with the surroundings. The polarity of particles and conveying pipe inner wall agrees reasonably well with the contact potential difference measurements. The perturbations in the capacitance signal due to charge accumulation are larger with smaller air superficial velocity. The denser flow regimes give larger wall residual charge. Wall charging process shows similar trend described by surface potential taken from electrostatic voltmeter to that revealed by ECT measurements. Also the addition of small amount (0.5% by weight) of anti-static agent (Larostat-519) in the powder form decreases the electrostatic charge generation by altering the dynamics of particle-particle and the particle-wall collisions. (C) 2004 Elsevier Ltd. All rights reserved.