| IFM Consulting Oy | Professional & scientific | 2025 |
| Inoram OY | Wholesale & retail | 2025 |
| Inu Finland OY | Real estate | 2007 |
| Io-Media OY | Information & communication | 2012 |
| IS Capital Oy | Financial services | 2022 |
| IS Group Oy | Financial services | 2022 |
| IS Kiinteistöt Oy | Real estate | 2006 |
| IS Works Oy | Manufacturing | 1992 |
| IT-Palvelut Norén Oy | Information & communication | 2008 |
| IT-Palvelut Toni Viertomanner Oy | Information & communication | 2020 |
| ITALINNA Consulting Oy | Professional & scientific | 2023 |
| IV-Huolto Peltola Oy | Construction | 2023 |
| Ibocan Oy | Hospitality | 2023 |
| Ida Aaltonen Oy | Wholesale & retail | 2017 |
| Ideakuva Lepomäki Kommandiittiyhtiö | Professional & scientific | 1980 |
| Idearäätäli Oy | Professional & scientific | 1994 |
| Ideavisio Oy | Education | 2019 |
| Ihana Hamam Oy | Wholesale & retail | 2019 |
| Ihanat Kasvitaulut Ky | Manufacturing | 2012 |
| Ihmislääkärit Oy | Health & social care | 2018 |
| Iivarin Värit Oy | Construction | 2022 |
| Ikihonka Invest Oy | Real estate | 2013 |
| Ikitalo Oy | Construction | 2017 |
| Ikkunamies OY | Construction | 2010 |
| Iletek Engineering Oy | Professional & scientific | 2014 |
| Ilkka Kuuri-Riutta Ky | Administrative & support | 1999 |
| Ilmastointi Salminen Oy | Construction | 2006 |
| Ilmastointi ja Pelti Hakala Oy | Construction | 2011 |
| Ilonat Nisander Oy | Health & social care | 2014 |
| Ilpon Kone Oy | Wholesale & retail | 1990 |
| Improbatur Oy | Financial services | 2026 |
| Indigo Invest Oy | Financial services | 2007 |
| Indikator Pro Oy | Professional & scientific | 2022 |
| Industrial Maintenance Group Oy Ltd | Manufacturing | 2007 |
| Infralogistic Finland Oy | Construction | 2026 |
| Inframare-Maretech Oy | Construction | 2024 |
| Infura Oy | Information & communication | 2021 |
| Inkeri Alina Oy | Education | 2022 |
| Innokas media Ky | Information & communication | 2017 |
| Inpro-Sijoitus Oy | Real estate | 2002 |
| Insaine Oy | Wholesale & retail | 2026 |
| Inscon Oy | Construction | 2002 |
| Insinööritoimisto Antti Lehtilä Oy | Construction | 2006 |
| Insinööritoimisto Controllplan Oy | Professional & scientific | 1992 |
| Insinööritoimisto EcoPlan Oy | Professional & scientific | 2012 |
| Insinööritoimisto Estec Oy | Real estate | 2016 |
| Insinööritoimisto Huunanmaa Ky | Construction | 1995 |
| Insinööritoimisto Kustannussalpa Osuuskunta | Professional & scientific | 1996 |
| Insinööritoimisto Pirttimäki Oy | Information & communication | 2024 |
| Insinööritoimisto Porin Korjausvalvonta Oy | Construction | 2007 |
| Insinööritoimisto Protekno Oy | Professional & scientific | 1986 |
| Insinööritoimisto Takuutalo Oy | Construction | 2011 |
| Insinööritoimisto Tarmo Peltoniemi Oy | Financial services | 1995 |
| Insinööritoimisto Unto Rantanen Oy | Construction | 1984 |
| Insinööritoimisto Vahekoski Oy | Construction | 2024 |
| Inspec Group Oy | Professional & scientific | 2026 |
| Inspon Group Oy | Wholesale & retail | 2018 |
| Integral Foresight Finland Oy | Professional & scientific | 2019 |
| Inter Handling Pori Oy | Transport & logistics | 2009 |
| Intravia Valmennus Oy | Professional & scientific | 2010 |
| Invest Ascendo Oy | Financial services | 2015 |
| Invisor Oy | Manufacturing | 2022 |
| Ipelift Oy | Transport & logistics | 2011 |
| Ironcode Oy | Information & communication | 2022 |
| Iser-Trans Oy | Wholesale & retail | 1992 |
| Iso-Ojan Liikenne Oy | Transport & logistics | 2021 |
| IsoIlo Oy | Wholesale & retail | 2020 |
| Isojoen Tuontiosa Oy | Wholesale & retail | 1992 |
| Isolinnan Hammaslääkärit Oy | Health & social care | 2025 |
| Isomaan Vesiosuuskunta | Water & waste | 2014 |
| Isoniittu - Riisvilja - Kellahti vesiosuuskunta | Water & waste | 1991 |
| Isännöinti Kotitar Oy | Real estate | 2013 |
| Isännöinti Leivo Oy | Real estate | 2005 |
| Isännöinti- ja Tilipalvelu Porin Balanssi Ky | Professional & scientific | 1991 |
| Itäreimarin Kotihoito Oy | Health & social care | 2015 |
| Itätullin Liikekiinteistö Oy | Real estate | 1983 |
| J & K Kuljetusliike Oy | Transport & logistics | 2021 |
| J & V Saneeraus & Puhdistus Oy | Construction | 2008 |
| J Huhtaviita Oy | Financial services | 2021 |
| J Johansson Service Ky | Other services | 2001 |
| J Vaistomaa Oy | Professional & scientific | 2014 |
| J ja T Koskinen avoin yhtiö | Wholesale & retail | 2011 |
| J&J Enqvist Oy | Wholesale & retail | 2025 |
| J&P Rauta Oy | Wholesale & retail | 2022 |
| J-P Uusitalo OY | Financial services | 2023 |
| J. Juhola Oy | Financial services | 2019 |
| J. Kivistö Oy | Transport & logistics | 2014 |
| JAL Kaivuu Oy | Other services | 2016 |
| Janmir Limited, Suomen Sivuliike | Construction | 2017 |
| JAS Control Oy | Professional & scientific | 2008 |
| JATO Rakennus Oy | Construction | 2012 |
| JAV-kaupat Oy | Wholesale & retail | 2019 |
| JB-Rengas Oy | Wholesale & retail | 2015 |
| JE-Planning Ky | Professional & scientific | 2006 |
| Jemracon OY | Construction | 2020 |
| JH Investment Oy | Real estate | 2022 |
| JH Monitoring Oy | Real estate | 2015 |
| JH Property Oy | Administrative & support | 2000 |
| JJ Pohjonen Oy | Financial services | 2023 |
| JJV Management Oy | Construction | 2019 |