|1940||Nihon Tennen Gas Kogyo Co., Ltd. was established in Yotsuya, Shinjuku-ku, Tokyo with a plant in Shirako, Chosei-gun, Chiba. Started production of natural gas and glass using the natural gas.|
|1944||Acquired Nihon Kansui and started manufacturing iodine, bromine, salt, etc.|
|1954||Started production of potassium iodide.|
|1957||Concluded a friendship agreement concerning natural gas supply with Toyo Koatsu Kogyo Co., Ltd. (currently Mitsui Chemicals, Inc.).|
|1961||Started supplying household gas to Shirako Municipal Gas (currently Shirako Municipal Gas Office).|
|1962||Established iodine production technology using ion exchange resin through joint research with Nippon Organo Shokai Co., Ltd. (currently Organo Corporation).|
|1963||Completed Koji plant.|
|1966||Changed iodine production from activated carbon technology to ion exchange resin technology.|
|1969||Established new iodine adsorption plant in Yokoshiba-machi, Chiba.|
|1974||Obtained capital participation from Tomen Corporation. (currently Toyota Tsusho Corporation).|
|1978||Completed development of Hanuki area (1 plant, 10 wells).|
|1989||Completed development of Kobayashi area (1 plant, 8 wells).|
|1993||Completed automation of mining facility and iodine production facility.|
|1995||Obtained capital participation from Kanto Natural Gas Development Co., Ltd.|
|1996||Obtained ISO9002 certification for the production of iodine and potassium iodide.
Changed the company name to Nihon Tennen Gas Co., Ltd.
|2003||Obtained ISO9001 certification for the production of iodine and potassium iodide.|
|2006||Acquired Kujukuri plant from Kanto Natural Gas Development Co., Ltd.|
|2007||Became a consolidated subsidiary of Kanto Natural Gas Development Co., Ltd.|
|2010||Completed new blowing-out tower for iodine production in Chiba plant.|
|2011||Supplied potassium iodide for stable iodine tablets as the only manufacturer in Japan during the nuclear emergency caused by the Great East Japan Earthquake.|
|2014||Became a group company of K&O Energy Group Inc.|
|2015||Completed new office building in Shirako-machi.
Completed first phase of development in the Kayaba area (1 plant, 5 wells).
|2016||Moved head office from Nihonbashi, Chuo-ku, Tokyo to Shirako-machi, Chiba.|
|2017||Completed the second blowing-out tower in Chiba plant.|
|2019||Completed blowing-out tower in Kujukuri plant.|
|2022||Restructured business with Kanto Natural Gas Development Co., Ltd. and changed the company name to K&O Iodine Co., Ltd.|