The effect of solid particles on micromixing has been studied using the competitive iodide/iodate reaction system in stirred, multi-impeller, solid-liquid systems. The influences of particle size, impeller speed, solid holdup, feed position, and energy input have been investigated. The change of the segregation index with the power input was more distinguishable only for the 450600m particles as compared with the large ones, at the same solid holdups. Also, for the small ones, cloud formation was observed at a particle concentration of 12.1wt%. However, the influence of larger particles of 11.25mm on micromixing was negligible, though both energy input and solid loading were increased. Besides, the optimal feed position was identified, and multiple feeds were also explored.