The micromixing efficiency of viscous media in a rotating packed bed (RPB) was evaluated by using the Dushman-Villermaux reaction system and was quantitatively analyzed based on the segregation index. The effects of the fluid viscosity, diameter of the packing wire, reactant concentration, rotational speed, and liquid flow rate on the mixing efficiency were evaluated. The results show that the segregation index decreases with an increase in the rotational speed, liquid flow rate, and Reynold number. Moreover, the segregation index declines with a decrease in the fluid viscosity, diameter of the packing wire, and reactant concentration. Furthermore, the micromixing time was calculated to be within 5.3 x 10(-5)-6x10(-4) s (for the viscosity range 1.01-219.18 mPa.s) based on the incorporation model. The micromixing efficiency in a Tee mixer with the same mesh packing was also evaluated. Compared with the Tee mixer and some other reactors, the RPB is superior for enhancing the micromixing efficiency, especially for higher-viscosity systems.