The Reflux Classifier is an innovative device offering advantages in both particle size classification and gravity separation. The system is a combination of a conventional fluidised bed and sets of parallel inclined plates as used to achieve a high throughput in a lamella settler. A reflux action develops as a result of fluidised particles segregating onto the inclined plates, and returning to the fluidised zone below. This in turn generates improved separation per ormance. A kinematic analysis that accounts for the high throughput of the device is presented. Experimental results showing the size classification of glass sphere particles (-200+20 mum) are presented, demonstrating the performance of the device.