A simple and effective classification method, the ’chute’, has been developed for the liquid-phase removal of fines from a batch of porous (catalyst) particles in the micrometre range. The chute is a continuous sedimentation fractionator, working in the gravitational field. Equations based an the sedimentation of particles were derived for the particle size distribution density function at a given position on the chute as a function of the initial size distribution density function. The particle size distribution on the chute appears to be only a function of the physical constants of the fluid, the particles and the dimensions of the chute. To verify the model equations, experiments with the chute were carried out at different suspension flows and chute angles. It was found that the experimental particle size distribution density functions at various positions on the chute were predicted reasonably well. Due to local disturbances near the bottom of the chute, the experimental curves exhibit a less sharp cut-off in the particle size distribution density function than was predicted by the model equations.