The segregation pattern of particles in circulating fluidized beds, 0.097 m and 0.150 m in diameter and 3 m in height, was investigated by using two groups binary solid particles that are different in diameter and density. The influence of operating conditions on the extent of particle segregation were examined. An empirical correlation for describing the extent of segregation was proposed. For distinguishing the segregation/mixing flow pattern, a theoretical criterion was derived and a segregation diagram was then prepared.