Effects of superficial gas velocities to a draft tube, to an annulus section and particle size on the solid circulation rate (Gs) have been determined in an internally circulating fluidized bed (0.28 m I.D.×2 m high) with an orifice type draft tube. The solid circulation rate from the draft tube to an annulus section increases with increasing gas velocities to the draft tube (Ud) and annulus section (Ua) and consequent increase in pressure drop across the orifice (ΔPor). However, the values of Gs decrease by 7-21% with increasing particle size from 86 to 288 μm. The pressure drop across the orifice increases with increasing Ud and Ua. However, ΔPor decreases by 5-23% with increasing particle size. To predict Gs in an internally circulating fluidized bed, a correlation is proposed as a function of ΔPor.