| TezLift Oy | Transport & logistics | 2025 |
| Thai Burpha Oy | Hospitality | 2021 |
| Thai Chili Kitchen Oy | Hospitality | 2024 |
| Thai Kinnua Ravintola Oy | Hospitality | 2022 |
| Thai-Helsinki Food & restaurant Oy | Hospitality | 2021 |
| Thaibob OY | Hospitality | 2024 |
| Thalassa Oy | Wholesale & retail | 2000 |
| Thales DIS Finland Oy | Manufacturing | 1990 |
| Thatguydigital Oy | Wholesale & retail | 2026 |
| The ARC ARORA COLLECTIVE Oy | Arts & recreation | 2024 |
| The Coffee Spot Oy | Hospitality | 2025 |
| The Empire of W Oy | Wholesale & retail | 2013 |
| The Flying Dutchman Nomad Brewing Company Oy | Wholesale & retail | 2015 |
| The Forge Platform Oy | Information & communication | 2025 |
| The Heartcores & Co. Oy | Education | 2024 |
| The Human Touch Robotics Oy | Professional & scientific | 2019 |
| The Idea Group HKI Oy | Hospitality | 2025 |
| The Middle of Nordic Ltd Oy | Wholesale & retail | 2005 |
| The One Finn Oy | Education | 2021 |
| The Packaléns Oy | Arts & recreation | 2024 |
| The School of European Swordsmanship Oy | Arts & recreation | 2008 |
| The Small Retail Oy | Wholesale & retail | 2020 |
| The Swatch Group (Nordic) AB, Suomen sivuliike | Wholesale & retail | 2001 |
| The Tekniikkatehdas Oy | Information & communication | 2017 |
| The Truth and Belief Oy | Professional & scientific | 2023 |
| The Unit Oy | Administrative & support | 2017 |
| The Valspar (Finland) Corporation Oy | Wholesale & retail | 2007 |
| The Yellow Line Oy | Transport & logistics | 1991 |
| TheNextDock Oy | Information & communication | 2020 |
| TheSand Oy | Water & waste | 2025 |
| TheWaste Oy | Professional & scientific | 2024 |
| Thellness Oy | Financial services | 2023 |
| Theme and Taste Oy | Hospitality | 2026 |
| Themistoklis Oy | Wholesale & retail | 2020 |
| Themo Nordic Oy | Professional & scientific | 2020 |
| Theorema Scandinavia AB, filial i Finland | Wholesale & retail | 2004 |
| Thermo Fisher Diagnostics Oy | Wholesale & retail | 2002 |
| Thermo Fisher Scientific Oy | Manufacturing | 1993 |
| Think Done Enterprise Oy | Administrative & support | 2025 |
| Third Nibble Oy | Information & communication | 2024 |
| Threedom Oy | Information & communication | 2024 |
| Threshold Events Oy | Arts & recreation | 2024 |
| Thrival Oy | Other services | 2025 |
| Throne Oy | Transport & logistics | 2018 |
| TiCons Oy | Professional & scientific | 2017 |
| TiPS Kenttä Oy | Arts & recreation | 2016 |
| Tiainen Elsaari Oy | Financial services | 2026 |
| Tiaisen Toteemit Oy | Construction | 2019 |
| Tiana Investment Oy | Financial services | 2024 |
| Tianbao Oy | Hospitality | 2013 |
| Tianix Oy | Wholesale & retail | 2024 |
| Ticson Oy | Information & communication | 2013 |
| TideNord Oy | Wholesale & retail | 2026 |
| Tidy place ky | Administrative & support | 2003 |
| Tiedekauppa Magneetti Oy | Wholesale & retail | 1989 |
| Tiedostava Mieli Oy | Health & social care | 2023 |
| TiedänMiehen Oy | Wholesale & retail | 2020 |
| Tieteks Oy Tieto- ja Tekstipalvelu Ahtiainen & Tervonen | Professional & scientific | 1999 |
| Tieto Card Services Oy | Administrative & support | 2007 |
| TietoHaukat Oy | Information & communication | 2014 |
| TietoWeb Oy | Information & communication | 2010 |
| Tietoset Components Oy | Wholesale & retail | 2025 |
| Tietotili Audit Oy | Professional & scientific | 1994 |
| Tietotili Invest Oy | Real estate | 2021 |
| Tietoviisto Oy | Education | 2022 |
| Tietäjä Labs Oy | Information & communication | 2026 |
| Tietäväinen Enterprises Oy | Professional & scientific | 2007 |
| Tiger Sport Oy | Arts & recreation | 2015 |
| Tigers Group Oy | Administrative & support | 2020 |
| Tii-Push Avoin yhtiö | Administrative & support | 1990 |
| Tiikerit Salibandy Oy | Arts & recreation | 2025 |
| Tiikman Group Oy | Construction | 2021 |
| Tiikman Oy | Construction | 2014 |
| Tiilikainen Holding Oy | Financial services | 2022 |
| Tiinan pesula Oy | Other services | 2024 |
| Tiinapmu OY | Other services | 2023 |
| Tiirk Oy | Construction | 2022 |
| Tiivistekeskus Oy | Wholesale & retail | 1993 |
| Tiivistetekniikka Oy | Wholesale & retail | 1993 |
| Tikkabit Oy | Information & communication | 2013 |
| Tikkanen Asianajotoimisto Oy | Professional & scientific | 2025 |
| Tikku Rakennus Oy | Construction | 2022 |
| Tikkurila Oyj | Manufacturing | 1917 |
| Tikkurilan Asemakeskus Oy | Real estate | 1989 |
| Tikkurilan Asemakeskuspysäköinti Oy | Real estate | 2012 |
| Tikkurilan Burger Oy | Hospitality | 2003 |
| Tikkurilan Golfkeskus Oy | Arts & recreation | 1988 |
| Tikkurilan Hot Wings Oy | Hospitality | 1992 |
| Tikkurilan Kahvila Oy | Hospitality | 2025 |
| Tikkurilan Kopiopalvelu Oy | Administrative & support | 1989 |
| Tikkurilan Kunnon Kauppa Oy | Wholesale & retail | 1981 |
| Tikkurilan LVI Oy | Construction | 2026 |
| Tikkurilan LVI-Palvelu Oy | Construction | 1990 |
| Tikkurilan Maanrakennus Oy | Construction | 1965 |
| Tikkurilan Metalli Oy | Wholesale & retail | 1994 |
| Tikkurilan Paino Oy | Manufacturing | 2018 |
| Tikkurilan Romu Oy | Wholesale & retail | 1977 |
| Tikkurilan Sähkö Oy | Construction | 2001 |
| Tikkurilan Tiikeri Areena Oy | Education | 2001 |
| Tikkurilan Tilitoimisto Oy | Professional & scientific | 1989 |