| Imatran Seudun Sähkönsiirto Oy | Energy | 2003 |
| Imatran Taksi Oy | Transport & logistics | 1974 |
| Imatran Talokeskus Oy | Real estate | 1979 |
| Imatran Talopalvelu Oy | Administrative & support | 2025 |
| Imatran Tapasravintolat Oy | Hospitality | 2021 |
| Imatran Tennishalli Oy | Arts & recreation | 2009 |
| Imatran Terästalo Oy | Real estate | 2006 |
| Imatran Teräsvalmiste Oy | Manufacturing | 2006 |
| Imatran Tilikonsultit Oy | Financial services | 2014 |
| Imatran Toimitilat Oy | Real estate | 2011 |
| Imatran Työterveys Oy | Health & social care | 2018 |
| Imatran Uimahallikahvio P.A.T. Ky | Hospitality | 2004 |
| Imatran Ulkoaluepalvelu Oy | Administrative & support | 1990 |
| Imatran Varaosakeskus Oy | Wholesale & retail | 1983 |
| Imatran Veturipalvelu Oy | Transport & logistics | 1994 |
| Imatran Vuokra-asunnot Oy | Administrative & support | 1989 |
| Imatran Vuokrapalvelu Oy | Administrative & support | 2020 |
| Imatran sähköasennus Oy | Construction | 2010 |
| Imatranajo Oy | Arts & recreation | 2019 |
| Imatrankosken Rauta Ky | | 1984 |
| Imatum Oy | Professional & scientific | 2021 |
| Immola Air Oy | Transport & logistics | 1983 |
| Imobis Oy | Information & communication | 2015 |
| Inaudio Oy | Wholesale & retail | 1989 |
| Industria One Oy | Professional & scientific | 2022 |
| Industrieersatzteile und Wartung Suomi Oy | Manufacturing | 1987 |
| Inkeritili Oy | Professional & scientific | 2010 |
| Inobo Asennus Oy | Other services | 2021 |
| Insinööritoimisto E & P Räikkönen OY | Professional & scientific | 2007 |
| Insinööritoimisto Harri Kokko Ky | Professional & scientific | 2004 |
| Invecom Oy | Wholesale & retail | 2018 |
| IronLakeTwo Oy | Energy | 2023 |
| Ismo Lahtela Oy | Wholesale & retail | 1996 |
| Isot 47 Avoin yhtiö | Hospitality | 2015 |
| Itä-Suomen Kiinteistöhuolto Ky | | 1984 |
| Itämajoitus Oy | Hospitality | 1990 |
| J-Line Oy Ltd | Wholesale & retail | 1995 |
| J. Rouhiainen Oy | Transport & logistics | 2021 |
| J. Wallenius Capital Oy | Health & social care | 2013 |
| J.Laatoitus oy | Construction | 2025 |
| JEE JEE Talo Oy | Real estate | 1989 |
| JL-Piipariset Oy | Real estate | 2017 |
| JPA Yhtiöt Oy | Professional & scientific | 1991 |
| JPM-Kaluste Oy | Wholesale & retail | 2005 |
| JPR Invest Oy | Financial services | 2020 |
| JS-Kalusto Oy | Administrative & support | 2025 |
| JS-Puu Oy | Construction | 2010 |
| JS-Sepät Ky | Wholesale & retail | 1982 |
| JS-Toimitilat Oy | Real estate | 2019 |
| JSJ-Metalli Ky | Manufacturing | 2007 |
| JVT Tekninen Oy | Other services | 2022 |
| Jaana-Transport Oy | Transport & logistics | 2003 |
| Jamokit Oy | Administrative & support | 2021 |
| Janisa avoin yhtiö | Wholesale & retail | 2017 |
| JarBar Oy | Hospitality | 2009 |
| Jarpaali Oy | Water & waste | 2019 |
| Javanainen Forge Oy | Manufacturing | 2017 |
| Jebaccon Oy | Professional & scientific | 2019 |
| Jee Jee Moto Oy | Real estate | 2010 |
| Jekku-Petteri Oy | Hospitality | 2011 |
| Jemi Rakennus Oy | Construction | 2007 |
| JoMaRak Oy | Construction | 2025 |
| JoSoleilOne PMC Oy | Real estate | 2023 |
| JoSoleilTwo Oy | Energy | 2023 |
| Jopsutin Oy | Arts & recreation | 2025 |
| Juha-Pekka Aarnio Oy | Wholesale & retail | 2011 |
| Jukan Lasipalvelu Oy | Manufacturing | 2007 |
| Jyrä-Sähkö Oy | Construction | 1991 |
| Järvikalastus Turtiainen Ky | Agriculture & fishing | 2001 |
| Jäsenkorjaus Imatra Oy | Real estate | 1979 |
| Jääsken vesiosuuskunta | Water & waste | 1999 |
| K & B avoin yhtiö | Hospitality | 2016 |
| K-konehuolto T. Irtamo Ky | Manufacturing | 1990 |
| KK Haapaselkä Oy | Manufacturing | 2017 |
| KL-Kuormaus Kari Lamberg Ky | Transport & logistics | 1991 |
| Kornermedia OY | Transport & logistics | 2010 |
| KOSKI Konditoria Oy | Hospitality | 2012 |
| KOy Imatran Palokuja 2 | Real estate | 2019 |
| KR-Putki Oy | Construction | 2019 |
| KT-Taberna Oy | Wholesale & retail | 2020 |
| Kaakkois-Suomen sähköasennus Ky | Construction | 2011 |
| Kaakon Energia Oy | Energy | 1998 |
| Kaakon Logistiikkapalvelut Oy | Transport & logistics | 2000 |
| Kaakon Raivauslinja Oy | Agriculture & fishing | 2003 |
| Kaakon Tili- ja Kiinteistöpalvelut Oy | Professional & scientific | 2024 |
| Kaakon Vakuutus Oy | Financial services | 2008 |
| Kaakon Verhoilu Oy | Other services | 1999 |
| Kaakon Veturipalvelu Oy | Transport & logistics | 2018 |
| Kaher Oy | Financial services | 1986 |
| Kahvila Karhuntupa Ky | Hospitality | 2012 |
| Kaivin- ja kiinteistöpalvelu Villanen Ky | Construction | 2003 |
| Kakkoskuljetus Ky | Transport & logistics | 1991 |
| Kalevanpoika Oy | Construction | 2019 |
| Kalle Kuronen ja Kumpp Oy | Real estate | 1980 |
| KarBar Oy | Hospitality | 2018 |
| Karjalan Hirsirakennus Oy | Construction | 2013 |
| Karjalan Katsastus Oy | Professional & scientific | 2025 |
| Karjalan Koneurakointi ja Korjaamo Oy | Construction | 2024 |
| Karjalan Muoviteollisuus Oy | Manufacturing | 1990 |
| Karjalan Piirakka Oy | Manufacturing | 2008 |