Abstract: In this paper, the gas-liquid flow in interstices formed bysimple cubic lattice packing of spherical particles in a trickle-bed reactor is analyzed on the scale of particle size. Starting from the basic hydrodynamic equations of motion, a microscopic one-dimensional model is established. Numerical solution of the model leads to the liquid distribution over the particle and the total liquid hold-up in the trickling flow regime. By analysing the stability of liquid film on the particle surface, a criterion is proposed to predict the transition from trickling to pulsing flow. Comparison of the model prediction with available experimental data suggests the usefulness and generality of the hydrodynamic model proposed for trickle-bed reactors.