| Insightish Labs Oy | Information & communication | 2024 |
| Insinööriasennus Oy | Construction | 1977 |
| Insinööritoimisto - Ingenjörsbyrå Brännäs Oy Ab | Professional & scientific | 2020 |
| Insinööritoimisto A Mäkelä Oy | Professional & scientific | 2026 |
| Insinööritoimisto Aavat Oy | Professional & scientific | 2014 |
| Insinööritoimisto Antti Kuikka Oy | Professional & scientific | 2003 |
| Insinööritoimisto Bertel Ekengren Oy | Construction | 2012 |
| Insinööritoimisto CAD-Company Finland Oy | Professional & scientific | 1994 |
| Insinööritoimisto Enermin Oy | Professional & scientific | 1978 |
| Insinööritoimisto Femdata Oy | Professional & scientific | 1981 |
| Insinööritoimisto Finins Oy | Professional & scientific | 2007 |
| Insinööritoimisto Helsingin Projektisuunnittelu Oy | Professional & scientific | 1986 |
| Insinööritoimisto Hirvilammi Oy | Professional & scientific | 2022 |
| Insinööritoimisto Hyppänen & Schrey Oy | Professional & scientific | 2022 |
| Insinööritoimisto JARVE Oy | Professional & scientific | 2006 |
| Insinööritoimisto Jar Oy | Information & communication | 1997 |
| Insinööritoimisto Juhani Kiiras Ky | Professional & scientific | 2017 |
| Insinööritoimisto Jussi Linnakangas Oy | Professional & scientific | 1984 |
| Insinööritoimisto K. Parila Oy | Professional & scientific | 2018 |
| Insinööritoimisto KW-Help Oy | Professional & scientific | 2011 |
| Insinööritoimisto Kaj Saarnio Oy | Professional & scientific | 2011 |
| Insinööritoimisto Kari Oy | Transport & logistics | 2014 |
| Insinööritoimisto Keinonen Ky | Professional & scientific | 1990 |
| Insinööritoimisto Konstru Oy | Professional & scientific | 1993 |
| Insinööritoimisto Levy Oy | Professional & scientific | 2018 |
| Insinööritoimisto M.J. Lehti Oy | Construction | 1993 |
| Insinööritoimisto Matti Janhunen Oy | Professional & scientific | 2018 |
| Insinööritoimisto Oy Material Konsult Ab | Professional & scientific | 2000 |
| Insinööritoimisto P Laamanen Oy | Professional & scientific | 1992 |
| Insinööritoimisto Pentti Savolainen Oy | Professional & scientific | 1989 |
| Insinööritoimisto Planmax Oy | Professional & scientific | 2018 |
| Insinööritoimisto Pontek Oy | Professional & scientific | 1966 |
| Insinööritoimisto R. Yli-Houhala Oy | Professional & scientific | 1989 |
| Insinööritoimisto R.B.H Systems Oy | Professional & scientific | 1996 |
| Insinööritoimisto Saniera Oy | Professional & scientific | 1993 |
| Insinööritoimisto Seppo Levy Oy | Professional & scientific | 1989 |
| Insinööritoimisto Setalaj Oy | Professional & scientific | 2004 |
| Insinööritoimisto Sydänmaanlakka Ky | Professional & scientific | 2003 |
| Insinööritoimisto Taurus Oy | Professional & scientific | 1983 |
| Insinööritoimisto Telar Oy | Professional & scientific | 1990 |
| Insinööritoimisto Timo Rantakokko & Co Oy | Professional & scientific | 1975 |
| Insinööritoimisto Timo Vasa Oy | Financial services | 1994 |
| Insinööritoimisto Toikka Oy | Manufacturing | 1991 |
| Insinööritoimisto Tuotepuu Oy | Professional & scientific | 1993 |
| Insinööritoimisto Vainikka Oy | Construction | 1990 |
| Insmat Oy | Wholesale & retail | 1989 |
| Inspiraatioliiga Oy | Professional & scientific | 2024 |
| Inspire Connect Oy | Professional & scientific | 2025 |
| Inspire Group Oy | Professional & scientific | 2005 |
| Inspire it Oy | Professional & scientific | 1992 |
| Inspiro Advisors Oy | Professional & scientific | 2023 |
| Inspiro Consulting Oy | Professional & scientific | 2004 |
| Install Team Oy | Other services | 2023 |
| Instant Aim Oy | Professional & scientific | 2016 |
| Instantscore Oy | Financial services | 2019 |
| Instinctive Ventures Oy | Financial services | 2022 |
| Inston Oy | Professional & scientific | 2020 |
| Instru Optiikka Oy | Wholesale & retail | 2002 |
| Instructio Oy | Information & communication | 2024 |
| Instructura Oy | Real estate | 2011 |
| Insurro Oy | Information & communication | 2021 |
| Int.Trade, Yousry Ramadan Ky | Wholesale & retail | 1992 |
| Intalent Oy | Professional & scientific | 2024 |
| Intangibles Management Finland Oy Ab | Professional & scientific | 1997 |
| IntegraVia Oy | Health & social care | 2026 |
| Integral Oy | Information & communication | 2005 |
| Integrate Us Oy | Professional & scientific | 2018 |
| Integrity Consulting Oy | Information & communication | 2018 |
| Intel Finland Oy | Wholesale & retail | 1980 |
| IntelTek AI Oy | Information & communication | 2018 |
| Intelligent Consulting Engineers OÜ Suomen sivuliike | Professional & scientific | 2022 |
| Intelligent Globular Trading Oy | Manufacturing | 2016 |
| Intelligent Systems Oy Finland | Information & communication | 1992 |
| Intelligent Vantage Oy Ltd | Information & communication | 2021 |
| Intellipocket Oy | Information & communication | 2009 |
| IntentForm Oy | Information & communication | 2025 |
| Inteq Oy | Information & communication | 2019 |
| Inter Casa Consulting ICC Oy | Real estate | 1993 |
| Inter Electric Oy | Professional & scientific | 2012 |
| Inter House Painting Oy | Construction | 1989 |
| Inter Lattiat Oy | Construction | 1996 |
| Inter-Gruppe Oy | Professional & scientific | 1991 |
| Inter-Hinaus Oy | Transport & logistics | 2020 |
| Inter-Psyko Oy | Health & social care | 1989 |
| Interactive Auto Media Oy | Professional & scientific | 2008 |
| Interbaltic Investments Oy | Financial services | 1992 |
| Interbau Oy | Financial services | 1990 |
| Intercast Oy Ab Ltd | Professional & scientific | 1986 |
| Intercession Oy | Professional & scientific | 1985 |
| Interfast Oy | Professional & scientific | 1987 |
| Interfinnmerc Oy | Wholesale & retail | 1993 |
| Intergalactic Solutions Oy | Administrative & support | 2019 |
| Interim Management Finland IMF Oy | Administrative & support | 2005 |
| Interior Design Latvalahti Oy | Professional & scientific | 2022 |
| Interior Oriental Oy | Wholesale & retail | 2025 |
| Interleaf Oy | Professional & scientific | 1989 |
| Interline Oy | Administrative & support | 1990 |
| International Asset Management IAM Oy | Education | 2016 |
| International Beauty Solutions Passo Oy | Wholesale & retail | 2021 |
| International Consulting Paalu Oy | Health & social care | 1991 |