| Isännöitsijätoimisto Seppo Simola Oy | Real estate | 1984 |
| Isännöitsijätoimisto Siljamäki Oy | Real estate | 2017 |
| Isännöitsijätoimisto T.L. Johansson Oy | Real estate | 2010 |
| Isännöitsijätoimisto Talon Isäntä Oy | Real estate | 2003 |
| Isännöitsijätoimisto Westerstråhle & Co Oy Ab | Real estate | 1975 |
| Isäntien Oy | Financial services | 2022 |
| It's Alive Films Oy | Information & communication | 2013 |
| It's Alive Productions Oy | Information & communication | 2008 |
| It's Oona Oy | Other services | 2025 |
| It's so Fab! Oy | Wholesale & retail | 2016 |
| Itabu Oy | Information & communication | 2017 |
| Italian Stone Rakennuspalvelut Oy | Construction | 2016 |
| Italianfest Oy | Arts & recreation | 2022 |
| Itamaa Oy | Professional & scientific | 2010 |
| Itara Oy | Professional & scientific | 2018 |
| Ite Invest Oy | Real estate | 2020 |
| Itech International Oy | Information & communication | 2021 |
| Iterator Oy | Information & communication | 2008 |
| Itgoes Oy | Wholesale & retail | 2024 |
| Itio Consulting Oy | Professional & scientific | 2020 |
| Itis Car Group oy | Other services | 2024 |
| Itis autokorjaamo oy | Other services | 2025 |
| Itkotrade Consulting Oy | Professional & scientific | 2025 |
| Itok Oy | Wholesale & retail | 1992 |
| Itrum Oy | Information & communication | 2003 |
| Itsapil Oy | Professional & scientific | 2019 |
| Itsybitsy Commerce Oy | Administrative & support | 2026 |
| Itsybitsy Group Oy | Professional & scientific | 2025 |
| Itu Biodyn Oy | Wholesale & retail | 2018 |
| Itu Design Oy | Professional & scientific | 2007 |
| Itu Insights Oy | Professional & scientific | 2018 |
| Itu Robotics Oy | Manufacturing | 2016 |
| Itua Oy | Information & communication | 2004 |
| Itunen Oy | Professional & scientific | 2014 |
| Itä Automaalari Oy | Other services | 2019 |
| Itä-Helsingin Autohuolto Oy | Other services | 2025 |
| Itä-Helsingin Autokorjaamo Oy | Other services | 2020 |
| Itä-Helsingin Burger Oy | Hospitality | 2002 |
| Itä-Helsingin Jalkapalloareenat Oy | Arts & recreation | 2011 |
| Itä-Helsingin Lasi Oy | Construction | 1987 |
| Itä-Helsingin Maanrakennus Ky | Real estate | 2014 |
| Itä-Helsingin Rakennuspalvelut Oy | Construction | 2021 |
| Itä-Helsingin Seniorihoiva Oy | Health & social care | 2014 |
| Itä-Helsingin Toimistopalvelu Oy | Professional & scientific | 1986 |
| Itä-Jollaksen investointi Oy | Professional & scientific | 2020 |
| Itä-Pasilan Pysäköinti Oy | Transport & logistics | 1982 |
| Itä-Suomen Hoitokodit Oy | Health & social care | 1992 |
| Itä-Suomen Liikennekasvatus Oy | Education | 1990 |
| Itä-Uudenmaan Palvelukoti Oy | Health & social care | 1998 |
| Itäcouscous Oy | Information & communication | 2022 |
| Itähelsingin Ravintolat Oy | Hospitality | 2012 |
| Itäinen & Co Oy Ab | Professional & scientific | 2025 |
| ItäkadunFENNIA Oy | Hospitality | 2025 |
| Itäkeskuksen Burger Oy | Hospitality | 1995 |
| Itäkeskuksen Burgerexpress Oy | Hospitality | 2002 |
| Itäkeskuksen Kukka Oy | Wholesale & retail | 1993 |
| Itäkeskuksen Poliklinikka Oy | Health & social care | 1992 |
| Itäkeskuksen Suutari ja Avainpalvelu Oy | Other services | 1992 |
| Itäkeskuksen fysikaalinen hoitolaitos Hannu Nurminen Ky | Health & social care | 1981 |
| Itäpaja Oy | Information & communication | 2010 |
| Itärata Oy | Transport & logistics | 2022 |
| Itäväylän Hammaslääkärit Oy | Health & social care | 1984 |
| Itäväylän Vauhti Oy | Professional & scientific | 2023 |
| Iuris Nova Oy | Education | 2003 |
| Ivalor Oy | Construction | 2023 |
| Ivan Enterprise Oy | Hospitality | 2010 |
| Ivehe Oy | Financial services | 2018 |
| Ivesting OY | Real estate | 2021 |
| Ivia Oy | Administrative & support | 2020 |
| Ivlivs Capital Oy | Financial services | 2026 |
| Ivlivs Oy | Financial services | 2025 |
| Ivors Construction Oy | Construction | 2011 |
| Ivory Luxe Heaven Oy | Other services | 2024 |
| Ivory Rock Oy | Financial services | 2024 |
| Ivy Pay Oy | Financial services | 2022 |
| Iwaru Oy | Professional & scientific | 2010 |
| Ixion Computer Oy | Wholesale & retail | 1989 |
| Ixir-verkkokurssit Oy | Education | 2021 |
| Ixxus Finland Oy | Administrative & support | 2023 |
| Iyuno A/S, Suomen sivuliike | Information & communication | 2004 |
| Izakaya BenjaMino Oy | Hospitality | 2021 |
| Izarra Oy | Professional & scientific | 2013 |
| Izm Oy | Professional & scientific | 2026 |
| IÅK Partners ab oy | Financial services | 2009 |
| J & A Agency Oy | Professional & scientific | 2014 |
| J & A Kulta Ky | Wholesale & retail | 1985 |
| J & A Savolainen Oy | Wholesale & retail | 2004 |
| J & M Laine Oy | Other services | 1986 |
| J & M Parhiala Oy | Real estate | 1972 |
| J & M Perälä Oy | Wholesale & retail | 1901 |
| J & P Heinonen Oy | Wholesale & retail | 2008 |
| J & R Invest Oy | Professional & scientific | 2018 |
| J & S Palvelut Oy | Other services | 2023 |
| J & T Kodinhoitajat Oy | Health & social care | 2003 |
| J & T Rakentajat Oy | Construction | 1976 |
| J Autio Oy | Wholesale & retail | 1991 |
| J Export Oy | Transport & logistics | 2009 |
| J Innovation Oy | Administrative & support | 2021 |
| J Kliini Oy | Professional & scientific | 2024 |
| J Minkkinen Consulting Oy | Professional & scientific | 2007 |