The market today requires the industry to transition from mass production to personalized production, where every product is made and customized for its client. As a result, the need for large-volume reactors is decreasing, and millireactors are emerging as a potential replacement for them. The space for millireactors is most prevalent in fine industries such as the pharmaceutical and chemical industries, as they are characterized by excellent substance and heat transfer, which in itself conditions more efficient and better used systems. The addition of static mixers to the millireactor can result in further process improvement. The aim of this paper was to show static mixers used in industry and to create a millireactor with a constructed geometry of static mixers and conduct a Fenton reaction in them. Millireactors were fabricated by the additive manufacturing process called stereolithography. The tube millireactor without static mixers was used as a reference, while the other millireactor had static mixers installed. Fenton reaction was performed in millireactors and the yield was calculated by the ratio of molar flow rates at the beginning and end of the reaction. During the Fenton reaction with a fixed retention time, a regular increase in conversions was observed with an increase in retention time. The yield of the reaction increases proportionally with the length of the reaction as expected. The better performance of the tube millirector relative to the millireactors with static mixers is caused by dead volumes that eliminate mixing and most likely the stability of the chemicals used in the reaction is insufficient.