| Year | Detail |
| 1941 |
Mitsui Chemical Industry was established. |
| 1955 |
Mitsui Petrochemical Industries was established. |
| 1960 |
DuPont and Mitsui Chemicals form Mitsui Polychemicals (currently DuPont- Mitsui Polychemicals). |
| 1965 |
Osaka Petrochemicals established. |
| 1976 |
Mitsui Toatsu Chemicals Inc. and Mitsui & Co. Ltd. established Mitsui Toatsu Fine Chemicals Inc. |
| 1987 |
Mitsui Chemicals Singapore established. |
| 1988 |
Mitsui Chemicals America established. |
| 1990 |
Mitsui Chemicals Europe established. |
| 1997 |
Mitsui Petrochemicals Industries Ltd. and Mitsui Toatsu Chemicals Inc. merge to form Mitsui Chemicals Inc. |
| 2000 |
Osaka Petrochemicals became a wholly-owned subsidiary. |
| 2002 |
Mitsui Sumitomo Polyolefin Co. Ltd. starts business operation. |
| 2005 |
Mitsui Kagaku Platech merges with Hi-Sheet Industries to form Mitsui Chemicals Fabro Inc. |
| 2006 |
Yamamoto Chemicals Inc. became a wholly-owned subsidiary. |
| 2009 |
Tohcello Co. Ltd. became a wholly-owned subsidiary. |
| 2011 |
Acquisition of Acomon AG. |
| 2014 |
Acquisition of Corning Incorporated’s SunSensors operations. |
| 2018 |
Acquired ARRK Corporation. |
| 2023 |
Mitsui Chemicals and Sanyo Chemical established a Limited Liability Partnership (LLP) for PPG Production. |