| HyväKiertää Oy | Administrative & support | 2017 |
| I-S Terästekniikka Oy | Manufacturing | 1989 |
| IB Invest Oy | Financial services | 2007 |
| ICSL Mastery Oy | Professional & scientific | 2008 |
| IH Site Service Oy | Construction | 2008 |
| IT Zone Oy | Information & communication | 2026 |
| Ivolga Media OY | Professional & scientific | 2017 |
| Ikaalisten Ravintolaliike Oy | Hospitality | 2023 |
| Iloinen Ilme Oy Savonlinna | Hospitality | 2017 |
| IlonTassut Oy | Wholesale & retail | 2020 |
| Iltakoti Oy | Health & social care | 2014 |
| Imupalvelu Luukkainen Ky | Water & waste | 1977 |
| InBeat Oy | Information & communication | 2018 |
| InInform Oy | Information & communication | 2016 |
| Industria Center Oy | Wholesale & retail | 1990 |
| Industrial Apps Oy | Information & communication | 2020 |
| Infra Wise Oy | Professional & scientific | 2021 |
| Inno Group Oy | Wholesale & retail | 2010 |
| Inno Tekniikka Oy | Wholesale & retail | 2024 |
| Innocel Oy | Professional & scientific | 2021 |
| Insinööritoimisto Kaartinen Oy | Professional & scientific | 2016 |
| Insinööritoimisto Marttila Oy | Professional & scientific | 2013 |
| Interlink Oy | Professional & scientific | 1996 |
| Invelop Oy | Manufacturing | 1987 |
| Inverion Oy | Professional & scientific | 2024 |
| Iskes Invest Oy | Administrative & support | 2026 |
| Isännöinnin Sydän Oy Isännöinti- ja tilipalvelu | Real estate | 2016 |
| Isännöinti Taloluotsi Oy | Real estate | 2018 |
| Itä-Suomen Kauppapojat avoin yhtiö | Wholesale & retail | 2000 |
| Itä-Suomen Kylmälaitepalvelu Oy | Wholesale & retail | 1998 |
| Itä-Suomen Metallikierrätys Oy | Wholesale & retail | 2023 |
| Itä-Suomen Pesutiimi Oy | Other services | 2018 |
| Itä-Suomen Rakennuskuivaus Oy | Construction | 2009 |
| Itäinen Asema Oy | Real estate | 2015 |
| Itäväylän Auto-, Sähkö- ja Konekorjaamo Kommandiittiyhtiö | Other services | 1996 |
| Ivial Oy | Professional & scientific | 1999 |
| J & J Maku Oy | Hospitality | 2018 |
| J & N Nauska Oy | Professional & scientific | 2012 |
| J Kosonen Oy | Professional & scientific | 2021 |
| J&J Group Service Oy | Administrative & support | 2021 |
| J&J Rakentajat Oy | Construction | 2021 |
| J-PAK Holding Oy | Administrative & support | 2022 |
| J. Nousiainen Service Oy | Manufacturing | 2013 |
| J. Valppu Oy | Construction | 2012 |
| Jengissä OY | Arts & recreation | 2026 |
| JESC Holding Oy | Real estate | 2018 |
| JJP Ratkaisut Oy | Administrative & support | 2022 |
| JK Herkku Oy | Manufacturing | 2011 |
| JKE-Louhinta Ky | Construction | 2004 |
| JKJ Ravintolat OY | Hospitality | 2005 |
| JLMM Invest Oy | Financial services | 2025 |
| JM Ironworks Oy | Construction | 2024 |
| JMPS Engineering Oy | Manufacturing | 2023 |
| JOPE Holding Oy | Administrative & support | 2021 |
| JPL Tilintarkastus Oy | Administrative & support | 2017 |
| JPT Transport Oy | Transport & logistics | 2018 |
| JS Motohelp Oy | Other services | 2020 |
| JS Saneeraus ja Peltipalvelu Oy | Construction | 2021 |
| JT Freetime Oy | Hospitality | 2018 |
| JT.Street Oy | Hospitality | 2026 |
| JTJ-Works avoin yhtiö | Administrative & support | 2019 |
| Jaaskjo1 Oy | Construction | 2026 |
| Jaky Oy | Manufacturing | 1990 |
| Jalkaterapiakeskus OrthoPodo Oy | Health & social care | 2005 |
| Jamux Oy | Construction | 2024 |
| Janwall Oy Ltd | Manufacturing | 2008 |
| Janze Oy | Professional & scientific | 2002 |
| Japikoti Oy | Construction | 2022 |
| Jargon Oy | Information & communication | 1995 |
| Jarkko Tapanila Oy | Wholesale & retail | 1990 |
| JarkkoKekki Oy | Wholesale & retail | 2003 |
| Jessica K Oy | Wholesale & retail | 2007 |
| Jevet Oy | Arts & recreation | 2020 |
| Ji Lin Oy | Hospitality | 2017 |
| Johanna Tapanila Oy | Professional & scientific | 1987 |
| Jorman liikenne ja Taxi palvelut Oy | Transport & logistics | 2015 |
| Jst-rak Oy | Construction | 2023 |
| Jukumu Oy | Arts & recreation | 2021 |
| Juridixhelp Oy | Hospitality | 2014 |
| Juuri Markkinointi Oy | Professional & scientific | 2024 |
| Jyrki Seppä Oy | Administrative & support | 2020 |
| Järki Kiinteistöt Oy | Real estate | 2020 |
| Järvi-Suomen Edunvalvonta Oy | Other services | 2021 |
| Järvi-Suomen Mansikat Oy | Agriculture & fishing | 2020 |
| JärviSuomen LVI & Rakentamispalvelut Oy | Construction | 2018 |
| Järvikuljetus M Papunen Oy | Professional & scientific | 1990 |
| KHC Systems Oy | Construction | 2024 |
| KL-Louhinta Oy | Construction | 2022 |
| KM Huoltopalvelut Oy | Other services | 2012 |
| KNG-Konsultointi Oy | Professional & scientific | 2018 |
| KOY Savonlinnan Olavinkatu 15 | Real estate | 2025 |
| KPK works oy | Agriculture & fishing | 2025 |
| KVM Etelä - Savo Oy | Wholesale & retail | 2019 |
| Kaakkois-Suomen Invest Oy | Financial services | 2021 |
| Kahvila Saima Oy | Hospitality | 2011 |
| Kahvila Tuju Oy | Hospitality | 2007 |
| Kahvila-Grilli Aarresaari Avoin yhtiö | | 1998 |
| Kaihdinlinna Oy | Wholesale & retail | 2009 |
| Kakkukaaos Oy | Manufacturing | 2023 |
| Kala Behm Oy | Agriculture & fishing | 2020 |