In 1939, a factory was established as the intermediates production base for dyes and pharmaceuticals by Japan Dyestuffs Manufacturing Co., which was founded in 1916 for the domestic production of synthetic dyes and eventually became the largest dyestuffs manufacturing company in Japan. Following the merger of this company with Sumitomo Chemical, the factory became Sumitomo Chemical's Oita Works in 1944. Subsequently the Works began the production of agricultural chemicals and in 1962 started manufacturing a pesticide known as Sumithion^TM, which has become popular not only in Japan but also in overseas markets. Using its advanced organic synthesis technologies, the Works is now engaged in the manufacture of a wide range of agricultural chemicals, resorcinol used in adhesives for tires and other applications, and a polymer additive called Sumilizer^TM GP. Also, the Works started production of oligonucleotide APIs in 2023, and small molecule APIs and intermediates in 2024 to enhance the manufacturing organization for pharmaceutical chemicals. The Oita Works is also home to the pharmaceuticals manufacturing plant of Sumitomo Pharma Co., Ltd., and plays a core role in the globalization of the Sumitomo Chemical Group's life science chemicals business.

In 1949, Sumitomo Chemical established a technology to industrially synthesize pyrethroid, a compound related to the insecticidal component contained in pyrethrums, and constructed a plant to manufacture PYNAMIN^TM on the premises of its former factory in Torishima, Osaka. Subsequently, in response to an increase in demand for the product, the company launched a new plant in 1978 in Misawa City, Aomori Prefecture. Since then, the Misawa Works has been playing an important role as the company's supply base from which a range of pyrethroid insecticides for household use, public hygiene, and agricultural use are exported to countries around the world.