- October 1, 2007
- Mitsui & Co. Steel Ltd. was inaugurated as Mitsui & Co. Steel Construction Material Ltd. changed its trade name to Mitsui & Co. Steel Ltd.
- April 1, 2008
- Merged with the following companies & unit: the domestic Iron & Steel Products team of Mitsui & Co. Ltd., Sintsuda Corporation,
Mitsui & Co. Special Steel Ltd., and Mitsui & Co. Plate Processing Ltd.
Relocated the head office to Akasaka Biz Tower, Akasaka, Minato-ku, Tokyo.
- September 1, 2010
- Established new Automotive Steel Unit as a result of business restructuring with Iron & Steel Products Business Unit of Mitsui & Co., Ltd.
- July 1, 2012
- Implemented organizational reforms and changed the names of various business units Construction Materials, Pipe & Plate Products Unit (formerly the 1st Business Division ), Steel Plate and Sheet Unit (formerly 2nd Business Division), Stainless Steel Unit (formerly Special Stainless Steel Materials Unit ), Steel Wire Rods, Products & Special Steel Unit (formerly Special Stainless Steel Materials Unit ), Automotive Steel Unit, Hokkaido Office (branch changed to regional office).
- April 1, 2013
- Steel scrap business activities taken over from Mitsui Bussan Metals Co., Ltd. and established new Ferrous Raw Materials Unit.
Established new Global Infrastructure Steel Business Division.
- October 1, 2014
- The newly established “Project Construction Materials Unit”.
- November 1, 2014
- The domestic construction materials business and metal scrap business of Mitsui & Co. Steel Ltd. were integrated with all businesses operated by Metal One Structural Steel & Resource Corporation, to form a new company called Metal One Mitsui Bussan Resource & Structural Steel Corporation.（holding 50% shares）
- April 1, 2015
- The Steel Plate & Sheet Unit is split to form two new units: “Steel Plate & Pipe Business Unit” and “Steel Sheet Business Unit.”
The tinplate domestic sales business is transferred from Mitsui & Co., Ltd. to the newly established “Steel Sheet Business Unit.”
The heavy plate trading business is transferred from Mitsui & Co., Ltd. to the newly established “Steel Plate & Pipe Business Unit.”
- April 1, 2017
- Newly established Flat Steel Products Global Trade Unit, transferred from Mitsui & Co., Ltd. handling an export business of Hot Rolled & Cold Rolled Steel, Tin Mill Products and Electrical Steel.
- April 1, 2018
- A part of the iron and steel products business is transferred to NIPPON STEEL & SUMIKIN BUSSAN CORPORATION.
Implemented organizational reforms and changed the names of various business units.
Automotive & Electrical Steel Unit (formerly Automotive Steel Business Unit), Project Construction Materials Unit (formerly Project ConstructionMaterials Unit, Steel Plate& Pipe Business Unit), Performance Steel Products Unit (formerly Steel Wire Rods, Products & Bearing Unit, Stainless & Special Steel Unit), Infrastructure Steel Products Unit (formerly Flat Steel Products Global TradeUnit, Steel Sheet Business Unit, Hokkaido Branch, Tohoku Branch, Niigata Branch), West-Japan Business Unit (formerly Osaka Office, Nakatsu Branch, Chugoku Branch, Shikoku Branch, Kyushu Branch), Chubu Business Unit (formerly Nagoya Office)
- October 1, 2020
- Newly established “Energy Steel Products Unit” was transferred from Mitsui & Co., Ltd. an energy materials business used for oil and gas development, production and transportation.