Axial dispersion of gas and solid phases in a gas-solid packed column at trickle flow, a promising new countercurrent operation, was evaluated using residence time distribution (RTD) experiments. The column was packed with dumped Pall rings, the gas phase was air at ambient conditions and the solid was a porous catalyst carrier.The RTD experiments for the solid phase were carried out using the “perfect pulse method”, while for the gas phase the “imperfect pulse method” was used. The model parameters were calculated by the methods of moments and various parameter optimization methods.At a given solid flow rate axial dispersion of the gas phase decreases with increasing gas velocity and is strongly dependent upon solid mass flux. Axial dispersion of the solid phase is approximately independent of the gas velocity and it is reduced if the solid mass flux is increased. For conditions of practical importance, 2 – 5 and 5 – 15 Pall ring layers correspond to the height of a mixing unit in the gas and solid phase, respectively.