| Sinisaari Energia Oy | Professional & scientific | 2024 |
| Sipilisti Oy | Administrative & support | 2016 |
| Sireenimaja Oy | Administrative & support | 2010 |
| Sirock Oy | Wholesale & retail | 1994 |
| Sirén Logistics Oy | Transport & logistics | 2018 |
| Sirén Yhtiöt Oy | Professional & scientific | 2007 |
| Sisu Akselit Oy | Manufacturing | 1998 |
| Sisustusarkkitehtitoimisto Katajala & Jurvelin Oy | Professional & scientific | 2018 |
| Sisustusrakennuskauppa Siraka Oy | Wholesale & retail | 2023 |
| Sisustustalo J.Lehmusto Oy | Wholesale & retail | 1991 |
| Sisäilmari Oy | Professional & scientific | 2013 |
| Sisärakenne Onni Oy | Construction | 2022 |
| Sivukadun Avopalvelu Oy | Health & social care | 2013 |
| Sixmix Oy | Wholesale & retail | 1994 |
| Skogster Ravintolat Oy | Hospitality | 2007 |
| SmileSet Oy | Information & communication | 2024 |
| So Unique Oy | Wholesale & retail | 2021 |
| So What Holding Oy | Financial services | 2017 |
| Sofil Oy | Professional & scientific | 2023 |
| Soft Insanity Oy | Information & communication | 2021 |
| Soihdunvartijat Oy | Arts & recreation | 2025 |
| Soini Hellsten Oy | Transport & logistics | 1986 |
| Soini Partners Oy | Health & social care | 2024 |
| Soittopojat Oy | Arts & recreation | 2021 |
| Solana Beats Ky | Health & social care | 1989 |
| Solariumstudio Sunbody Oy | Other services | 2011 |
| Sollon Kodit ja Kiinteistöt Oy | Construction | 2014 |
| SoloMotors Oy | Wholesale & retail | 2022 |
| Some Show Oy | Professional & scientific | 2024 |
| Somentekijät Oy | Professional & scientific | 2021 |
| Sonic Tools Oy | Manufacturing | 1995 |
| Soranjalostus Jaakonsaari Oy | Mining & quarrying | 1990 |
| Sostea Oy | Health & social care | 2016 |
| Sound Supreme Oy | Information & communication | 2005 |
| Sounds Like Media Oy | Arts & recreation | 2023 |
| Southwest Trade Oy | Wholesale & retail | 1990 |
| Sovulla Oy | Education | 2017 |
| Spira Oy Hengityshoitokeskus | Manufacturing | 1992 |
| Sport Fund GP I Oy | Financial services | 2019 |
| Sport Fund I Ky | Financial services | 2019 |
| Sport Fund Management Oy | Financial services | 2019 |
| SportaDoc Oy | Health & social care | 2026 |
| Sports Management Group SMG Ky | Arts & recreation | 1998 |
| Sporttiveikot Oy | Wholesale & retail | 1995 |
| Stand By - Tuotanto Ky | Administrative & support | 1990 |
| Star Capital Oy | Real estate | 2005 |
| Steakhouse Seta Oy | Hospitality | 2024 |
| Stoic Investments Oy | Financial services | 2026 |
| Stone Service Oy | Other services | 2016 |
| Studio Fenix avoin yhtiö | Other services | 2006 |
| Studio Mikaela Löfroth Oy | Professional & scientific | 2007 |
| Sulkahattu Oy | Financial services | 1989 |
| Sun NÄKYMÄ Oy | Professional & scientific | 2023 |
| Sun Sign oy | Professional & scientific | 2017 |
| Sun Sähköpalvelut Häme Oy | Construction | 2013 |
| Sunmarket Suomi Oy | Wholesale & retail | 2005 |
| Sunny Car Center Hämeenlinna Oy | Professional & scientific | 2010 |
| Suodatinpojat Oy | Construction | 2025 |
| Suomalainen Kiinteistö Oy | Real estate | 2006 |
| Suomen Autorahaksi Oy | Wholesale & retail | 2010 |
| Suomen Caravan Media Oy | Information & communication | 1990 |
| Suomen Country Hotellit Oy | Hospitality | 1999 |
| Suomen Fanisormi Avoin Yhtiö | Wholesale & retail | 2014 |
| Suomen Gastroenterologipalvelut Oy | Health & social care | 2022 |
| Suomen Isotermi Oy | Construction | 2007 |
| Suomen Kasarmin Aarteet Oy | Wholesale & retail | 2026 |
| Suomen Kenttäkone Oy | Administrative & support | 2011 |
| Suomen Lattiapinnoittajat Oy | Construction | 2020 |
| Suomen Liivineulomo Oy | Manufacturing | 2017 |
| Suomen Loisto Oy | Information & communication | 1998 |
| Suomen Mentaalivalmennus Oy | Professional & scientific | 2019 |
| Suomen Nettiasunnot Ky | Real estate | 2005 |
| Suomen Osuusvaruste | Transport & logistics | 2009 |
| Suomen Paikallisvalvoja Oy | Professional & scientific | 2022 |
| Suomen Puutarha-akatemia Oy | Administrative & support | 2021 |
| Suomen Rakennekartoitus OY | Professional & scientific | 2003 |
| Suomen Runkorakennus Oy | Construction | 2023 |
| Suomen Ruokakauppasijoitus Oy | Real estate | 2010 |
| Suomen SaPeS Oy | Administrative & support | 1987 |
| Suomen Tarjous Tavaratalot Oy | Wholesale & retail | 1994 |
| Suomen Tilausaktiviteetit Oy | Education | 1989 |
| Suomen Ulkoilupalvelu oy | Wholesale & retail | 2011 |
| Suomen Visiotalo Oy | Information & communication | 1989 |
| Suomen Yhteysturva Oy | Information & communication | 2024 |
| Suomen lääketieteellinen informaatiopalvelu Oy | Health & social care | 1990 |
| Suomen ovimarket Oy | Wholesale & retail | 2004 |
| Suomen rahoitusratkaisut Oy | Financial services | 2024 |
| Suostu Investments Oy | Financial services | 2009 |
| Supermedia ADV Oy | Professional & scientific | 1998 |
| Susannan Lihakauppa Oy | Wholesale & retail | 2024 |
| Suunnittelu Lapikisto Oy | Professional & scientific | 2019 |
| Suunnittelutoimisto Köhler Oy | Professional & scientific | 1995 |
| Suunterveys Siirola Oy | Health & social care | 2022 |
| Suutari Lahtinen Oy | Other services | 2023 |
| Suvantalo Oy | Real estate | 2012 |
| Suvero, avoin yhtiö | Wholesale & retail | 2001 |
| Suvi-Caravan Ky | Hospitality | 1989 |
| Suvituulen Vakuutus Oy | Financial services | 2024 |
| Sydeemi Oy | Professional & scientific | 2016 |
| Synaptic Oy | Information & communication | 1997 |