Abstract: Experimental study of phase characteristics in a high-density downer (5.6 m tall, 80 mm ID)is presented in this work.Phase time fractions was essentially uniform in the central region, and then increased with increasing(1-ε_av).Dense phase time fraction varied from 10% to 20%,and approximated to dilute phase time fraction.The axial size of dense phase in downer was about 10—15 mm, which was as large as tens times to one hundred times of particles diameter.The averaged solids concentration in the dense phase was as 1.7 times as the local solids concentration, while that in dilute phase was about 40%.The transformation from dense phase to dilute phase in the riser was a sharp transition, while for the downer such transition was gradual.Dense phase in downer was much more difficult to observe than in riser due to its shorter duration time, smaller size and lower density.