The effect of static mixer internals on the hydrodynamic properties and the axial gas mixing characteristics has been determined in a circulating fluidized bed riser of FCC catalysts. Two types of static mixer are used with the variation of superficial gas velocity and solid circulation rate. With the static mixer in the riser, the axial solid holdup is much higher than that without the static mixer and the bottom acceleration length is shortened. The axial gas dispersion coefficients in the riser decrease with increasing solid circulation rate with the R-R configuration static mixer.