| Insto Kaunisto Oy | Professional & scientific | 2018 |
| InteRitus Holding Oy Ltd. | Financial services | 2022 |
| Integrum Ky | Professional & scientific | 1982 |
| Intentface Oy | Information & communication | 2023 |
| Intentus Oy | Administrative & support | 2009 |
| Inter Handling Finland Oy | Transport & logistics | 2013 |
| Intera Software Oy | Information & communication | 2000 |
| Intercity Investor Oy | Construction | 1994 |
| Intercontrol Oy | Wholesale & retail | 2011 |
| Interdialogi Markkinointipalvelut Oy | Administrative & support | 1995 |
| Interen Oy | Wholesale & retail | 2019 |
| International Software Planners Skandinavia Oy | Information & communication | 1992 |
| Interplus Oy | Wholesale & retail | 1987 |
| Intervendor Oy | Hospitality | 1980 |
| Intexment Holding Oy | Financial services | 2019 |
| Intian Helmi Oy | Hospitality | 2019 |
| Into Mind Oy | Professional & scientific | 2016 |
| Intradex Oy | Hospitality | 1994 |
| Introgroup Oy | Professional & scientific | 2013 |
| Intuitio Oy | Information & communication | 2021 |
| Invcom Oy | Financial services | 1987 |
| Invest House Oy | Real estate | 2012 |
| InvestOiva Oy | Professional & scientific | 2001 |
| InvestPort Oy | Real estate | 2014 |
| Investare Oy | Real estate | 1998 |
| Investhink Oy | Professional & scientific | 2011 |
| Investime Oy | Financial services | 1987 |
| Investop Oy | Financial services | 2001 |
| Invo Future Oy | Real estate | 2006 |
| Inzego Oy | Professional & scientific | 2020 |
| Irepoint Oy | Manufacturing | 1995 |
| Iris Works Oy | Professional & scientific | 2017 |
| Iron Gate Management Oy | Financial services | 2025 |
| IronSales Oy | Professional & scientific | 2024 |
| Irtico Oy | Manufacturing | 1995 |
| Is-Ki Oy | Real estate | 2019 |
| IsLi Oy | Real estate | 2008 |
| Isaskar Invest Oy | Real estate | 2016 |
| Iseeviot Oy | Wholesale & retail | 2015 |
| Island Holding Ab | Financial services | 2024 |
| Iso-Heikkilän Autopaikoitus Oy | Real estate | 1988 |
| Isokangas Infrastructure Oy | Real estate | 2026 |
| Isoluodon huvilametsä Oy | Real estate | 1975 |
| Isosuon energia oy | Energy | 2022 |
| Isovahan Huolto Oy | Energy | 1987 |
| Isoympyrä Oy | Other services | 2015 |
| Ispico Oy | Real estate | 2020 |
| Isännöinti & Tilipalvelu Attentus Oy | Real estate | 2002 |
| Isännöinti Etappi Oy | Real estate | 1987 |
| Isännöinti Granberg Oy | Real estate | 1978 |
| Isännöinti Kai Johansson Oy | Real estate | 2026 |
| Isännöinti Ruori Oy | Real estate | 2022 |
| Isännöinti- ja tilipalvelu Tolvanen Oy | Real estate | 2007 |
| Isännöintipalvelu Haaristo & Yrjänheikki Oy | Real estate | 2017 |
| Isännöintipalvelu Nykänen Oy | Real estate | 1982 |
| Isännöitsijä- ja tilitoimisto Matti Päivärinta Ky | Real estate | 1984 |
| Isännöitsijätoimisto Kaikumäki Ky | Professional & scientific | 1989 |
| It's A plan Oy | Professional & scientific | 2019 |
| It's Happening! Productions Oy | Professional & scientific | 2022 |
| Italgreen Finland Oy | Arts & recreation | 2025 |
| Italian Team Installation Oy | Construction | 2015 |
| Itiksen Jalostus Oy | Financial services | 2014 |
| Itkonen & Kyrki | Information & communication | 2014 |
| Itäharjun Autopesu Oy | Other services | 2025 |
| Itäharjun Galaxy Oy | Hospitality | 2022 |
| Itäharjun Levy ja Lista Ky | Wholesale & retail | 1985 |
| Itäharjun Ravintola Oy | Hospitality | 2024 |
| Itäisenkadun Taidetarvike Oy | Wholesale & retail | 1990 |
| Itäkeskuksen Kehitys Oy | Financial services | 2014 |
| Itämeri Advisory Oy | Professional & scientific | 2016 |
| Itämeri Brothers Oy | Professional & scientific | 2026 |
| Ivate Oy | Financial services | 2024 |
| Ives Oy | Professional & scientific | 1993 |
| J & S Lahtinen Oy | Hospitality | 2021 |
| J Levonen Oy | Wholesale & retail | 2022 |
| J Varrela Consulting Oy | Health & social care | 2021 |
| J&J Hoivakiinteistöt Oy | Real estate | 2020 |
| J&J Installation Oy | Construction | 2022 |
| J-Isännöinti Oy | Real estate | 2009 |
| J-Sec Oy | Education | 2021 |
| J. Heiska Group Oy | Real estate | 2024 |
| J. Huunonen Oy | Wholesale & retail | 2009 |
| J. Lindqvist Oy | Professional & scientific | 2018 |
| J. Plusisaari Oy | Professional & scientific | 2023 |
| J. Äikäs Oy | Construction | 2026 |
| J.Pylvänen Oy | Wholesale & retail | 2024 |
| J.Sandberg Oy | Manufacturing | 2007 |
| J.V. Virtanen Oy | Professional & scientific | 2014 |
| J.W.N - Rakennus & Maalaus Ky | Construction | 2015 |
| J2L Invest Oy | Professional & scientific | 2022 |
| J3A Asunnot Oy | Real estate | 2021 |
| J3C Robotics Oy | Manufacturing | 2026 |
| J3ppo Oy | Professional & scientific | 2021 |
| JA-SU-Invest Oy | Financial services | 1996 |
| JA-SU-Service Oy | Professional & scientific | 2018 |
| JAG Oy | Construction | 1971 |
| JAK Nordic Oy | Professional & scientific | 1994 |
| JAKS Invest Oy | Real estate | 2005 |
| JAMIKSET Oy | Professional & scientific | 2025 |
| JAP-markkinointi Ky | Professional & scientific | 2009 |