| 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. |
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| 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. |