As an important intermediate, nitrosyl sulfuric acid (NSA) is widely used in diazotization in the fine chemical industry. However, the conventional gaseous SO 2 method in the Venturi tubular reactor has low reaction efficiency and high energy consumption due to insufficient gas−liquid contact. In this work, a rotating packed bed (RPB) reactor was first applied for the synthesis of NSA, in which a liquid SO 2 and HNO 3 reaction occurred. Effects of the rotational speed, reaction temperature, mole ratio of SO 2 /HNO 3 , and flow rate of SO 2 on the product quality and NSA yield were investigated. Results indicated that the NSA yield increased by 9.5% with the rotational speed from 100 r/ min to 500 r/min. Compared with the conventional Venturi reactor with gas−liquid reaction, the RPB reactor with a liquid− liquid reaction could reduce the volume of the reactor by 1 order of magnitude, quantity of equipment by 69%, steam consumption by 100%, and electricity consumption by 43%