When ultrasound is irradiated in liquid, a local reaction field with high temperature and high pressure, which is called a hot spot due to cavitation, is formed. In order to enhance the performance of a sonoreactor, it was considered to improve the liquid flow by a propeller set in the sonoreactor. With the placement position, the revolution speed and the number of blades of the propeller varied at the same liquid height and power input, a decolorization reaction of iodine in the presence of disodium hydrogenphosphate in a starch solution has been carried out in order to examine the effect of the mixing on the sonochemical reaction. The mixing by the propeller made the intrinsic chemical reaction field larger and the sonochemical reaction faster. The reaction rate became faster with an increase in the revolution speed of the propeller. At the same placement position and revolution speed, the reaction rate was much faster for a propeller with more blades.