| Suomen Asuntohankinta Oy | Real estate | 2010 |
| Suomen Energianeuvonta Oyj | Professional & scientific | 2011 |
| Suomen Energiavarat Oy | Financial services | 2009 |
| Suomen Helisoft Oy | Information & communication | 1992 |
| Suomen Juomalaitetukku Oy | Manufacturing | 2023 |
| Suomen Kalastusaluerekisteri Oy | Arts & recreation | 2017 |
| Suomen Karjapörssi Ky | Wholesale & retail | 1993 |
| Suomen Koboltti Oy | Mining & quarrying | 2016 |
| Suomen Rakennustutkimus Oy | Professional & scientific | 1955 |
| Suomen Scancoor Kristallisointi Oy | Construction | 1992 |
| Suomen Tankkilaivaosakeyhtiö | Financial services | 2000 |
| Suomen Tuontiliike Oy | Wholesale & retail | 2011 |
| Suomen Yritysvakuutus Oy | Financial services | 2012 |
| Superco HR Oy | Professional & scientific | 2021 |
| Susanna Grundström Oy | Education | 2024 |
| Suunnittelutoimisto Jenny Tunis Oy | Professional & scientific | 2013 |
| Suurholma Oy | Financial services | 2008 |
| Suvi-Grillari Ky | Hospitality | 1989 |
| Suvilahden Autopurkaamo Oy | Wholesale & retail | 1994 |
| Suvituuli SMH osuuskunta | Health & social care | 2017 |
| Svahntton Oy | Wholesale & retail | 1990 |
| Svecon Oy Ab | Professional & scientific | 2008 |
| Svedberga Plantskola Finland Ab | Wholesale & retail | 2025 |
| Svenska Bokhandeln Ab | Wholesale & retail | 2008 |
| Swahn Wasa Oy | Transport & logistics | 2022 |
| Swirl Ab | Financial services | 2024 |
| Switch Nordic Green AB Filial Finland | Energy | 2009 |
| Sydbottens Kontorsdata Ab | Information & communication | 1975 |
| Sydän Asunnot Oy | Real estate | 2016 |
| Syrian Market Oy | Wholesale & retail | 2023 |
| Sähköasennus Pohjanmaa Oy | Construction | 2016 |
| Sähköasennus Simo Saarela Oy | Construction | 2012 |
| Sähköinsinööritoimisto Ky Jaakko Sirviö & Co | Construction | 1973 |
| Sähköliike SähköWaasa Oy | Construction | 2003 |
| Sähköpalvelu Walberg Vaasa Oy Ab | Construction | 2017 |
| Sähkötyö Dahl Oy | Construction | 2021 |
| Sähkötyö Kovanen Oy | Construction | 2020 |
| Sähkötyö Myllymäki Oy | Construction | 2019 |
| Särkiniemi Invest Oy | Financial services | 2011 |
| Säästö-Viking Öljymäki Ky | Wholesale & retail | 1967 |
| Säätöpiste Oy Vaasa | Construction | 1990 |
| Södergran & Södergran Ab | Real estate | 1996 |
| T & A BidCo Oy | Real estate | 2020 |
| T & F Fisk Finland Ab | Wholesale & retail | 2026 |
| T & L Nordin Oy | Wholesale & retail | 2011 |
| T-Lähikulma Granholm Ky | Wholesale & retail | 1989 |
| T-lähikauppias Heino Ojanen Ky | Wholesale & retail | 1966 |
| T. Alanen Oy | Transport & logistics | 1995 |
| T. Lauttamus Oy | Wholesale & retail | 1993 |
| T1 Energy Finland JV Oy | Manufacturing | 2021 |
| T1 Energy Finland Oy | Manufacturing | 2021 |
| TAH Capital Oy | Financial services | 2026 |
| Taigor OY | Transport & logistics | 2023 |
| TALE Ab Oy | Hospitality | 2022 |
| TAPP Oy | Construction | 2024 |
| TAVA Solutions Oy | Information & communication | 2023 |
| Teok OY | Wholesale & retail | 2025 |
| TF-Talousratkaisut Oy | Professional & scientific | 2025 |
| THEO-Consult Ky | Professional & scientific | 2025 |
| TIU Investment Oy | Financial services | 2021 |
| TJK Tietolaite Oy | Information & communication | 1994 |
| TK Engineering Oy | Information & communication | 2003 |
| TK Rahoitus Oy | Financial services | 2014 |
| TM Leasing Oy Ab | Administrative & support | 2020 |
| TM-Teema Group Ky | Professional & scientific | 2008 |
| TM-Teema Oy | Real estate | 2019 |
| TMS Group Ab | Professional & scientific | 2016 |
| TOT-Holding Oy Ab | Financial services | 2023 |
| TS-Katto Oy | Construction | 2018 |
| TSR Install Vasa Ab | Construction | 2025 |
| TT Botnia Oy | Health & social care | 2019 |
| TX Autolasitalo Oy | Other services | 1990 |
| TYK Invest Oy | Financial services | 2022 |
| Tabita products Oy Ab | Wholesale & retail | 1992 |
| Taboada Enterprises Ab Oy | Other services | 2016 |
| Taco Taco Oy Ltd | Wholesale & retail | 2026 |
| Taiku Oy | Construction | 2021 |
| Taimi Holdings Oy | Real estate | 2025 |
| Taipalus Trading Oy | Wholesale & retail | 1982 |
| Taja Invest Oy | Financial services | 2016 |
| TajaTec Oy | Financial services | 2016 |
| Takkinen Capital Oy | Financial services | 2025 |
| Taksi 15 Vaasa Oy | Transport & logistics | 2018 |
| Taksi Ilkka Toppinen Oy | Transport & logistics | 2018 |
| Taksi Pentti Johan. Salminen Oy | Transport & logistics | 2001 |
| Taksi Team Laurilat | Transport & logistics | 2010 |
| Taksi-Salminen Oy | Transport & logistics | 2024 |
| Taksipalvelu Jonessi Oy | Transport & logistics | 2022 |
| Taksipalvelu Viitasalo Oy | Transport & logistics | 2012 |
| TalentMasterID Oy | Information & communication | 2026 |
| Talk 5 Oy | Financial services | 2000 |
| Tallskat vattenandelslag/ Tallskatin vesiosuuskunta | Water & waste | 2012 |
| Talopalvelu Westerqvist Ky | Administrative & support | 1996 |
| Talous- ja Lakikonsultointi Koskinen Oy | Professional & scientific | 1995 |
| Talous- ja assistenttipalvelut UnelmaS Ky | Professional & scientific | 2019 |
| Talouskonehuolto M. Pollari Oy | Other services | 1982 |
| Talso Oy | Financial services | 1993 |
| Tam-Koti Oy | Real estate | 2020 |
| Tammi Kiinteistötekniikka Oy | Real estate | 2010 |
| Tammivire Ky | Health & social care | 2001 |