A novel fluidized-bed coating process using the rapid expansion of supercritical fluid solutions (RESS) is described for the coating of fine particles. Experiments were conducted in a 50 mm i.d. circulating fluidized bed with an internal nozzle in the center of the riser. Microspheroidal catalyst particles (average particle size 56 mu m) were used as the core particles. Supercritical carbon dioxide solutions of paraffin were expanded through the nozzle into the bed that was fluidized by air. The coating mass and coating rates were measured by a sampling method. Mercury porosimetry was used to determine the quality of the coated particles. A stable coating of fine particles was achieved without the formation of agglomerates at room temperature. The present study examines the effects of hydrodynamics and solute concentration on coating rate and coating efficiency.