Experimental investigations on particle mixing in a larger spout-fluid bed with cross section of 1 m x 0.05 m and height of 4 m were carried out. The axial and radial distributions of tracer particle under different spouting gas velocities and fluidizing gas flow rates were measured. The particle mixing behaviors were studied according to the concentrations of tracer particles and flow patterns. Besides, the mechanism of particle mixing was preliminarily discussed. It is found that increase in spouting gas velocity and fluidizing gas flow rate can both promote the particle mixing in spout-fluid beds. Particle mixing in spout-fluid beds is due to three mechanisms: diffusion, transportation and circulation, and bubbles action. However, it changes significantly with increasing fluidizing gas flow rate and spouting gas velocity. Diffusion, transportation and circulation dominate the particle mixing at low fluidizing gas flow rates, while bubble actions dominant the particle mixing at large fluidizing gas flow rates. When increasing the spouting gas velocity, diffusion, transportation and circulation dominant the particle mixing. (c) 2007 Elsevier B.V. All rights reserved.