The Ehime Works was established in 1913 to produce sulfuric acid and calcium superphosphate from sulfur dioxide recovered from the emissions of the copper refinery operated by Sumitomo. Located in Ehime, in the Shikoku region of Japan, which is Sumitomo Chemical's place of origin, the Ehime Works has been transforming itself, keeping pace with the progress of the company. The Works began manufacturing industrial chemicals against the backdrop of the development of Japan's modern industries and entered the petrochemical field in 1958, ahead of the others. The Works has been proactively increasing the number of products it manufactures, although it suspended operation of its manufacturing facilities for ethylene and some ethylene derivatives in 1983. Its products now include bulk chemicals (e.g. caprolactam and methacrylate resin), fine chemicals such as methionine (feed additive), and electronics products such as optical functional films, which the Works manufactures using a variety of basic materials it produces. In 2009, the manufacturing facilities for optical functional films and other products became the Ohe Works and now functions independently. The Ehime Works responds flexibly to the development of new business and supports the company in a number of business operations.

After the Ehime Works, the Chiba Works started operating in the Keiyo industrial district in 1967 as Sumitomo Chemical's second petrochemical complex. In 1983, in accordance with the company's plan to reorganize and streamline its petrochemical business, the manufacturing operations for petrochemical products were consolidated at the Chiba Works. The Works enhanced its ability to manufacture existing products and succeeded in manufacturing some derivatives that had been produced at the Ehime Works, thereby further strengthening its competitive capabilities. At present, the Chiba Works is engaged in the manufacture of products in the field of synthetic resins, synthetic rubbers, and organic chemicals. It is committed to further improving and expanding its portfolio of high value-added products while developing new manufacturing technologies and supporting the major projects undertaken by Sumitomo Chemical in strategic locations such as Singapore and Saudi Arabia. The Works thus serves as the “mother plant” of the company's Essential & Green Materials Sector and plays the core role in the global development of the business.