Particles of two different densities can be continuously and rapidly separated by employing sink-float phenomenon in split-flow thin (SPLITT) cells using both centrifugal and gravitational fields. Separation of a binary mixture of submicron size latex beads differing in densities is achieved by feeding them as a suspension in a carrier liquid of intermediate density into a SPLITT cell subject to a centrifugal field. A steady state condition is rapidly achieved, and two particle types accumulate at opposing channel walls as they are carried by the laminar channel flow to two separate outlets. Similarly, micron size particles of two different densities are separated using a planar channel and the gravitational field. Equations are developed to predict throughput in terms of the number fractions of the separated particles determined by scanning electron microscopy. Experimental results from three SPLITT cell systems under different field and flow conditions are compared with theoretical predictions.