Ultrasonic is well-known to be helpful for the improvement of chemical reactions due to its acoustic cavitation. This work reports for the first time the use of ultrasonic to enhance micromixing and mass-transfer in a rotating packed bed (RPB) reactor. The ultrasonic probes were installed as stators on the cover of the RPB reactor. Comparisons of micromixing efficiency, effective interfacial area, and volumetric liquid-side mass-transfer coefficient in the RPB reactor with and without ultrasonic were investigated systematically. A discussion for the micromixing and mass-transfer improvement in the RPB reactor was given. Feasibility studies indicated that the relative segregation index decreasing, the relative effective interfacial area increasing, and the relative volumetric liquid-side mass-transfer coefficient increasing are 13.8%, 3.7%, and 5.5%, respectively.