Micromixing plays a crucial role in fast chemical reactions. The micromixing efficiency in a rotating packed bed (RPB) was first studied via a throughway method with specially designed RPB structure accompanied by adoption of the iodide-iodate reaction system as index to the micromixing efficiency. With sampling along the radial position, micromixing efficiency in different packing zones of RPB was detected and analyzed and the importance of the inlet region of the RPB; on micromixing was experimentally confirmed. The effects of different operating conditions (e.g., rotational speed, liquid flow rates, and reagent concentration) on segregation index (X-s) were also investigated. On the basis of micromixing theory and appropriate assumptions on energy dissipation rate, the micromixing time tau(m). in the RPB was evaluated to reach about 10(-4) s, almost equal to what we calculated based on the incorporation model. Compared with other mixing devices, the RPB has a distinct advantage in improving micromixing efficiency, and maybe of many novel applications in the chemical and related industries.