| Suomen Telakunnostus Oy | Professional & scientific | 2013 |
| Suomen Telesähkö Oy | Wholesale & retail | 2016 |
| Suomen Tilaturva Oy | Information & communication | 2017 |
| Suomen Toimitilahallinta Oy | Real estate | 2000 |
| Suomen Vakiokiinteistöt Oy | Real estate | 2019 |
| Suomen Verkkotuki Oy | Information & communication | 2010 |
| Suomen Vibrakone Oy | Wholesale & retail | 1998 |
| Suomen hyllynkorjaustekniikka Oy | Manufacturing | 2025 |
| Suomen laki- ja tilipalvelut Oy | Administrative & support | 2024 |
| Suomen terveydenhuoltokonsultointi Oy | Professional & scientific | 2015 |
| Suomen vakioilmastointi Oy | Construction | 2016 |
| Suomen yksityinen turvallisuusneuvosto Oy | Administrative & support | 2020 |
| SuomiJoutsen Oy | Professional & scientific | 2007 |
| Suparu Adventures Oy | Transport & logistics | 2025 |
| Suur- Helsingin Sähkö Oy | Construction | 2019 |
| Suur-Helsingin Kirvestyö Oy | Construction | 1989 |
| Swandor OY | Real estate | 2019 |
| Swennsson OY | Administrative & support | 2022 |
| Sylykly man Ky | Other services | 2009 |
| Sähkö Oy Helsinki | Construction | 2012 |
| Sähkö-Duo Oy | Construction | 1989 |
| Sähkö-Rymy Ky | Construction | 2012 |
| Sähkö-Sino Oy | Construction | 1989 |
| SähköLämmöX Oy | Construction | 2008 |
| Sähköpalvelu Malmberg Oy | Construction | 2010 |
| Sähköpalvelu Raittila Oy | Construction | 2023 |
| Sähkörae Oy | Construction | 2005 |
| T&E Investment Oy | Financial services | 2023 |
| T&J Autopesu Oy | Other services | 2024 |
| T&O Hemolex Oy | Wholesale & retail | 2023 |
| T&T Lämpöpumppuhuolto Oy | Construction | 2012 |
| T-Golf Oy | Other services | 2019 |
| Tafes OY | Wholesale & retail | 2026 |
| Taide Ja Kehyspaja Alanko OY | Wholesale & retail | 2023 |
| TAL Total Solutions Oy | Financial services | 2014 |
| TCOVA Oy | Professional & scientific | 1994 |
| Teksun OY | Hospitality | 2019 |
| Teräskatto OY | Construction | 2026 |
| TH Carpetit Ky | Wholesale & retail | 2000 |
| THannah Oy | Other services | 2020 |
| TI Innovations & Consulting Oy | Information & communication | 2025 |
| TIP Collections Designated Activity Company, Suomen sivuliike | Administrative & support | 2022 |
| TIP Trailer Services Finland AB | Administrative & support | 1981 |
| TK-Tilitaso Oy | Professional & scientific | 2024 |
| TKC-Styling Oy | Wholesale & retail | 1997 |
| TL-Putkihuolto Oy | Construction | 2025 |
| TLP Rakennus Oy | Construction | 2019 |
| TN Ventures Oy | Information & communication | 2013 |
| Top-Asennus OY | Construction | 2008 |
| Topre OY | Construction | 2005 |
| TP-Kotiremontit Oy | Construction | 2019 |
| TPEX Oy | Professional & scientific | 2015 |
| TR Holding Vantaa Oy | Financial services | 2021 |
| TR-Koneistus Oy | Other services | 1991 |
| TR-Line Oy (Finland) | Transport & logistics | 2013 |
| TS Kodit Oy | Real estate | 2019 |
| TS Logistics Oy | Transport & logistics | 2015 |
| TS Toimistopalvelut Oy | Administrative & support | 2012 |
| TSR Pam Industry Oy | Hospitality | 2007 |
| TUO-727 Oy | Information & communication | 2021 |
| Tahtiverkot Oy | Construction | 2025 |
| Taikanäppi Oy | Professional & scientific | 1995 |
| Takala SIS. Oy | Manufacturing | 2019 |
| Taksi Haapajoki Oy | Transport & logistics | 2016 |
| Taksikuljetus Petrus Anttila Oy | Transport & logistics | 2000 |
| Taksipalvelu JA-PE Oy | Transport & logistics | 2019 |
| Taksiteknokraatti Oy | Transport & logistics | 1962 |
| Talentadore Oy | Information & communication | 2014 |
| Talin Rakennus- ja Siivouspalvelu Oy | Administrative & support | 1997 |
| Talma Import Oy | Wholesale & retail | 2011 |
| TaloTaito Rakennus- ja Siivousyritys Oy | Construction | 2024 |
| Talogren Oy | Real estate | 2010 |
| Talopekat Oy | Construction | 2009 |
| Talosakke Oy | Real estate | 1981 |
| Talouden Taika Oy | Professional & scientific | 2025 |
| Taloushallinto Oy Helena Sinisalo | Professional & scientific | 1984 |
| Talram Oy | Construction | 2012 |
| Talvitie Bygg ja Teknik Oy | Construction | 2016 |
| Tammesta Oy | Construction | 2025 |
| Tanning kerava Oy | Health & social care | 2022 |
| Tansa Rakennus OY | Construction | 2024 |
| Tanssi vahvaksi Oy | Education | 2025 |
| Tanstroi Oy | Construction | 2023 |
| Tapimare Oy | Wholesale & retail | 1993 |
| Tapimer Oy | Wholesale & retail | 1985 |
| Tarkastuslaskenta Mörk Oy | Professional & scientific | 2008 |
| Tarpoma Oy | Information & communication | 1978 |
| Tarrame Finland Oy | Manufacturing | 2020 |
| Tasar Oy | Professional & scientific | 2024 |
| TaseSisCo Oy | Administrative & support | 2013 |
| Tasekirjailijat Oy | Education | 2020 |
| TasteOn Oy | Wholesale & retail | 2025 |
| Teadena Oy | Wholesale & retail | 2008 |
| Team - Siivous ja Hoiva Oy | Administrative & support | 1995 |
| Tecet Oy | Wholesale & retail | 2005 |
| Tee-Rakennus Oy | Construction | 2007 |
| Teerilä Oy | Real estate | 2004 |
| Teesaikan Sähkö Ky | Construction | 2012 |
| Tehosuu Oy | Health & social care | 2010 |
| Tekjep Oy | Professional & scientific | 2008 |