| Industrial innovations and improvements 3i Oy | Manufacturing | 2018 |
| Inferunt Oy | Financial services | 2025 |
| Infinity Rakennus Oy | Real estate | 2019 |
| Inflex Oy | Administrative & support | 2005 |
| Infoglove Services Oy | Information & communication | 2005 |
| Infrapalvelu Kautonen Oy | Professional & scientific | 2016 |
| Infrastar Oy | Construction | 2010 |
| Ingalsuo H & J Ky | Professional & scientific | 1991 |
| Inlean Creative Oy | Information & communication | 2016 |
| Inmalti Oy | Information & communication | 2017 |
| Inmedia Systems Oy | Professional & scientific | 2004 |
| Innate Oy | Health & social care | 2003 |
| Innocase Oy | Professional & scientific | 1993 |
| Innokalori Oy | Education | 2020 |
| Innomotics AB, sivuliike Suomessa | Manufacturing | 2023 |
| Innosta palvelut Oy | Professional & scientific | 2024 |
| Innostava Design Oy | Manufacturing | 2021 |
| Innotrans Oy | Wholesale & retail | 1990 |
| InnovaSet Oy | Wholesale & retail | 2021 |
| Innovantti Oy | Professional & scientific | 2017 |
| Innovative Animal Rehabilitation Academy Oy | Education | 2025 |
| Innoventa Oy | Wholesale & retail | 1986 |
| Inodont Oy | Health & social care | 2026 |
| Inovva Fi Oy | Professional & scientific | 2021 |
| Inserii Ky | Administrative & support | 1999 |
| Inside fi Oy | Wholesale & retail | 2008 |
| Insinöörisähkö kommandiittiyhtiö A. Hakala | Construction | 1977 |
| Insinööritoimisto Advacon Oy | Professional & scientific | 1986 |
| Insinööritoimisto ETC Oy | Professional & scientific | 2019 |
| Insinööritoimisto Gradientti Oy | Professional & scientific | 2004 |
| Insinööritoimisto Honkanen & Huumonen Oy | Professional & scientific | 1982 |
| Insinööritoimisto Iketek Oy | Professional & scientific | 2007 |
| Insinööritoimisto Jokinen Oy | Professional & scientific | 2018 |
| Insinööritoimisto Jussi Mäkelä Oy | Professional & scientific | 2004 |
| Insinööritoimisto Kai Kouvo Oy | Education | 2014 |
| Insinööritoimisto LVI-Lepistö Oy | Construction | 2014 |
| Insinööritoimisto Lanvet Oy | Professional & scientific | 1981 |
| Insinööritoimisto Lepistö Oy | Professional & scientific | 2019 |
| Insinööritoimisto Luukka Oy | Professional & scientific | 2017 |
| Insinööritoimisto PBG Oy | Construction | 2025 |
| Insinööritoimisto Pentti Laiho Oy | Manufacturing | 1978 |
| Insinööritoimisto Risto Castren Oy | Professional & scientific | 1974 |
| Insinööritoimisto S&A Oy | Professional & scientific | 2026 |
| Insinööritoimisto Scantra Oy | Construction | 1998 |
| Insinööritoimisto Stenholm Oy | Real estate | 2024 |
| Insinööritoimisto TAK-Plan Oy | Professional & scientific | 1992 |
| Insinööritoimisto Terho Koponen Ky | Construction | 1980 |
| Insinööritoimisto Tripletec Oy | Professional & scientific | 2012 |
| Insinööritoimisto Vakkila Oy | Wholesale & retail | 1991 |
| Insinööritoimisto Valvontaverstas Oy | Professional & scientific | 2015 |
| Insofa Oy | Manufacturing | 1999 |
| Inspiroiva Creative Oy | Information & communication | 2018 |
| Installer Suomi Oy | Construction | 2022 |
| Instotec Oy | Construction | 2020 |
| Interior 4 You Oy | Other services | 2010 |
| International Forest Advisors Oy | Professional & scientific | 2024 |
| International Psychological Services PsyCHEN Oy | Health & social care | 2011 |
| Interring Oy | Professional & scientific | 1980 |
| Intersabor Oy | Real estate | 1983 |
| Intohimohuoltamo avoin yhtiö | Health & social care | 2020 |
| Investment & Competence Oy | Professional & scientific | 2023 |
| Investria Oy | Financial services | 2014 |
| IotaGrid Oy | Information & communication | 2021 |
| Ipa-Pesu Oy | Other services | 1992 |
| Ipe-Peite Oy | Manufacturing | 1994 |
| Irmeli Nurmi Ky | Wholesale & retail | 2015 |
| Ironcoaching Oy | Education | 2010 |
| Isku Inspira Oy | Financial services | 2023 |
| Isku Interior Oy | Wholesale & retail | 2005 |
| Isku Invest Oy | Real estate | 2005 |
| Isku Koti Oy | Wholesale & retail | 2005 |
| Isku Spaces Oy | Wholesale & retail | 1990 |
| Isku-Yhtymä Oy | Financial services | 1961 |
| Iskukone Oy | Real estate | 1995 |
| Iskukone-Kiinteistöt Oy | Real estate | 1989 |
| Islanders Holdings Oy | Financial services | 2025 |
| Ismo Siitonen Ky | Wholesale & retail | 1981 |
| Isomäki Consulting Oy | Professional & scientific | 2016 |
| Isotalon Maansiirto Ky | Construction | 1986 |
| Isännöinti M. Liedes Oy | Real estate | 2024 |
| Isännöinti- ja hallintopalvelut Erikkilä Ky | Real estate | 2004 |
| Isännöinti-Duo Oy | Real estate | 2006 |
| IsännöintiGlow Oy | Real estate | 2023 |
| Isännöintikeskus Tammen Oy | Real estate | 2023 |
| Isännöintitoimisto Talopro Oy | Real estate | 1985 |
| Isännöitsijätoimisto J. Rautama Oy | Real estate | 2008 |
| Isännöitsijätoimisto Ruuth Oy | Real estate | 1987 |
| Itafix Oy | Real estate | 2006 |
| Italian Tiles Oy | Wholesale & retail | 2008 |
| Itsemast Oy | Information & communication | 2018 |
| Itsemast Shop Oy | Wholesale & retail | 2022 |
| Itä-Hämeen Liikenne Oy | Transport & logistics | 2024 |
| Ivan Koliban Ky | Transport & logistics | 2023 |
| Iwanna Oy | Wholesale & retail | 1990 |
| J Järvensivu OY | Construction | 2008 |
| J&J Food Oy | Hospitality | 2018 |
| J&M Palvelut Ky | Real estate | 2006 |
| J&N Myynti Oy | Wholesale & retail | 2020 |
| J-Steel Oy | Manufacturing | 2018 |
| J. Kaitila Oy | Construction | 2025 |