The elutriation of fine particles (group C or group A particles) from a fluidized bed of fine-coarse particle mixtures was investigated at a steady state. FCC, AL(OH)(3), limestone, alumina, SIC, PVC and silica sand particles in the range of 22.44 to 650 mum were used as the fluidized particles. The elutriation rate constant of particles increased with increase of particle size in the range of group C particles at the constant superficial gas velocity and decreased with increase of the particle size in the rage of group A and B particles. The particle size corresponding to the maximum elutriation rate constant Is defined as the critical particle size of the elutriation. The critical particle size decreases with increasing elutriated particle density and with increasing gas velocity. On the contrary, the critical particle size increases with increasing the mean diameter of bed particles. But, the coarse particle density has no effect on the critical particle size. An empirical equation is obtained to estimate the critical particle size.