| SFF Forest Oy | Financial services | 2017 |
| SFF Holding Oy | Financial services | 2017 |
| SFF Property Oy | Real estate | 2017 |
| SJR Holding Oy | Real estate | 2019 |
| SLT - Suomen Liikelahjatukku kommandiittiyhtiö | Manufacturing | 2002 |
| SMA Mineral Oy | Mining & quarrying | 1999 |
| SSP Kiinteistöt Oy | Real estate | 2024 |
| Steeljet OY | Other services | 2006 |
| Studio E-City Ky | Hospitality | 2006 |
| SV Technologies Oy | Professional & scientific | 2026 |
| Sadinmaa Holding Oy | Construction | 2020 |
| Sadinmaan Tila Oy | Agriculture & fishing | 2014 |
| Safar-Botnia Ky | Administrative & support | 1989 |
| Saga Borealis Oy | Health & social care | 2019 |
| SagaMaaret Ky | Manufacturing | 2017 |
| Saku Palander Ky | Wholesale & retail | 2022 |
| SalTek Oy | Professional & scientific | 2009 |
| Salomeka Oy | Financial services | 1986 |
| Salonki Luonnon Kauniit Ky | Other services | 2011 |
| Samar Oy | Transport & logistics | 2007 |
| Samenta Avoin yhtiö | Hospitality | 2018 |
| Samkes Oy | Transport & logistics | 2025 |
| Sammalpeuhan Fysiikkavalmennus Oy | Education | 2020 |
| Sammutinhuolto Redi Oy | Manufacturing | 2017 |
| Samuli Pohjanen Oy | Construction | 2015 |
| Sangen Oy | Manufacturing | 2015 |
| Sanmarked Korhonen Ky | Wholesale & retail | 2000 |
| Sargos Oy | Construction | 2024 |
| Sarte Oy | Construction | 2025 |
| Sauna på Gränsen Oy | Arts & recreation | 2025 |
| Savotan Kisälli Oy | Real estate | 1984 |
| SePen Ralliautoilu ja Elämys Oy | Administrative & support | 2005 |
| SepeSun Oy | Administrative & support | 2022 |
| Sevetin Teräsukko Oy | Real estate | 2019 |
| Sf-cliniken Oy | Other services | 2012 |
| Sf-cosmetics Oy | Wholesale & retail | 1985 |
| Sf-import Oy | Wholesale & retail | 2024 |
| Siivous HarjAnne Oy | Administrative & support | 2015 |
| Silcom Oy | Wholesale & retail | 2010 |
| Silly Goose Oy | Professional & scientific | 2022 |
| Simulan Tarha, Avoin yhtiö | Agriculture & fishing | 1980 |
| Siskel Oy | Administrative & support | 2024 |
| Sky Burger Oy | Hospitality | 2020 |
| Skyplus Oy | Real estate | 2016 |
| Skyroutine Oy | Wholesale & retail | 2025 |
| Smeds-Uistin Ky, Pauli J. Smeds | Manufacturing | 1980 |
| Smeds-Uistin Oy | Manufacturing | 2008 |
| Smitplan Oy | Professional & scientific | 2019 |
| Sportti-Settu Oy | Wholesale & retail | 1986 |
| Stainless Feel Oy | Manufacturing | 2026 |
| Steel-Air oy | Construction | 2019 |
| StenMilk Oy | Agriculture & fishing | 2018 |
| Stormet Oy | Manufacturing | 2012 |
| StrikeIT Oy | Information & communication | 2019 |
| Studio Blue Oy | Professional & scientific | 1987 |
| Subida Oy | Hospitality | 2011 |
| Sulpadel Oy | Arts & recreation | 2022 |
| Sumitutkimus Oy | Professional & scientific | 2009 |
| Sumituuli Oy | Energy | 2000 |
| Suomen Gigakuitu Oy | Construction | 2020 |
| Suomen Kuljetustilaukset Oy | Transport & logistics | 2015 |
| Suomen Kultareservi Oy | Wholesale & retail | 2019 |
| Suomen Sähkötekniikka Oy | Construction | 2022 |
| Suomen tili-, isännöinti- ja kiinteistöpalvelu Oy | Construction | 2002 |
| Susanna ja Jyrki Ruokanen avoin yhtiö | Wholesale & retail | 2023 |
| Suumestari Oy | Health & social care | 1977 |
| Sydämen Noste Oy | Education | 2017 |
| Synergy Services Oy | Education | 2021 |
| Synttärisankari Oy | Arts & recreation | 2023 |
| Syrjälän Sähkö Ky | Construction | 2000 |
| Systemworx Oy | Information & communication | 2019 |
| Sähkökangas OY | Construction | 2006 |
| Sähkö Kummu Oy | Construction | 2002 |
| Sähköasennus J.Ylimäinen Oy | Construction | 2021 |
| Sähköcentre Ky | Construction | 1987 |
| Sähköurakointi WEST-TECH Oy | Construction | 2001 |
| Sähköurakointi ja -suunnittelu Liisanantti Oy | Construction | 2014 |
| Säiliöliikenne A. Myllykoski Oy | Transport & logistics | 1991 |
| T Junes Oy | Wholesale & retail | 2013 |
| T P Vähä Oy | Administrative & support | 2019 |
| T Pyyny Oy | Construction | 2019 |
| T Ryymin Ky | Administrative & support | 2003 |
| T-Market Vesku, Avoin yhtiö | Transport & logistics | 1990 |
| T. Konola OY | Real estate | 2022 |
| TA-Korjausrakenne Oy | Construction | 1995 |
| TB-Huolto Laukkanen Oy | Wholesale & retail | 1980 |
| Tiltek Rakennus OY | Construction | 1994 |
| Titomet OY | Professional & scientific | 2010 |
| TJ-Autopalvelu Ky | Transport & logistics | 2004 |
| TJ-Pelti Oy | Construction | 2007 |
| TKR-Palvelut Ky | Professional & scientific | 2024 |
| TKT Siivouspalvelu Ky | Administrative & support | 2010 |
| TLVIP Group Oy | Financial services | 2025 |
| TM Pharma Oy | Wholesale & retail | 2015 |
| TMEK Oy | Professional & scientific | 2022 |
| TORMOTORS Ky | Other services | 2002 |
| Tornion Kama-Palvelut OY | Manufacturing | 2002 |
| Tornion Laskentapalvelu Ky | Professional & scientific | 2013 |
| Tornion Musiikki OY | Wholesale & retail | 2008 |
| TS Palvelut Oy | Construction | 2022 |