| Saimaa Fortis Oy | Professional & scientific | 2018 |
| Sakari Sales Oy | Professional & scientific | 2024 |
| Sakir avoin yhtiö | Hospitality | 2019 |
| Saksalanraitin vesiosuuskunta | Water & waste | 2008 |
| Sam Lehtinen Ky | Hospitality | 1982 |
| Samer Oy | Hospitality | 2004 |
| Sami Kirjavainen Ky | | 1981 |
| Samppa Ahtiainen Oy | Professional & scientific | 2010 |
| Samridhi Oy | Hospitality | 2023 |
| Saneeraus J.Maikkula Ky | Construction | 2006 |
| Saneerauspalvelu Ahokas Oy | Construction | 2021 |
| Sanomalehti Uusi Pohjois-Karjala Oy | Information & communication | 1989 |
| Santalahti Management Oy | Hospitality | 2025 |
| Santalahti Resort Oy | Hospitality | 1994 |
| Sapocca Sauna Oy | Other services | 2026 |
| Sapokan Helmi Kiinteistö Oy | Real estate | 1976 |
| Sapokan Moottorihuolto Oy | Other services | 1987 |
| Sarain Oy | Real estate | 2026 |
| Sarastuskoti Oy | Health & social care | 2016 |
| Sardar Ky | Hospitality | 2012 |
| Sari Hakkarainen Ky | Wholesale & retail | 2000 |
| Sat-Antenni Ky | Construction | 1990 |
| Sata-Apu Oy | Administrative & support | 2010 |
| Satamaveturi Oy | Hospitality | 2018 |
| Saukonkoti Oy | Real estate | 2021 |
| Sauninto Oy | Wholesale & retail | 2022 |
| Savikon Puutarha avoin yhtiö | Agriculture & fishing | 1985 |
| Scandigo Oy | Wholesale & retail | 2021 |
| Sea Element Oy | Transport & logistics | 2008 |
| Seal-Sec Oy | Wholesale & retail | 1986 |
| Sednove Oy | Professional & scientific | 1994 |
| Selpairent Oy | Wholesale & retail | 2003 |
| Sense Tec Oy | Wholesale & retail | 1988 |
| Sentiax Oy | Professional & scientific | 2001 |
| Seppo Tähtinen Ky | | 1986 |
| Serdaxet GH Oy | Other services | 2022 |
| Settek Oy | Construction | 2003 |
| Seven Group Oy | Real estate | 2003 |
| Sherwood Stable Oy | Arts & recreation | 2002 |
| Shinestorm Mentorship Oy | Education | 2024 |
| Shold Oy | Administrative & support | 2022 |
| Sievers Nordic Solutions Oy | Administrative & support | 2026 |
| Siivous- ja kiinteistöhuolto P. Kääriäinen Oy | Administrative & support | 1995 |
| Siivousliike Hel-Jo avoin yhtiö | Administrative & support | 1992 |
| Siivouspalvelu Eijamo Ky | Administrative & support | 1984 |
| Siivouspalvelu Hänninen Oy | Administrative & support | 2014 |
| Sisa Group Oy | Construction | 2026 |
| Sisu Scandi Group Oy | Wholesale & retail | 2025 |
| Sisustus Buumi Ky | | 1989 |
| Sisäpiiri Oy | Construction | 2003 |
| Skinnarin Kurssit avoin yhtiö | Information & communication | 1981 |
| SkyLED Finland Oy | Professional & scientific | 2018 |
| SnowWater Oy | Professional & scientific | 2018 |
| Social First Oy | Information & communication | 2021 |
| Sofeltech Oy | Manufacturing | 1990 |
| Sohvian Oy | Administrative & support | 2026 |
| Soiniset Kiinteistöt Oy | Financial services | 2017 |
| Soiwa Acoustics Oy | Manufacturing | 2024 |
| Sol Trivium Oy | Professional & scientific | 2016 |
| Solamen Oy | Other services | 2026 |
| Solid Trade Oy | Wholesale & retail | 2021 |
| Solid Way Oy | Transport & logistics | 2013 |
| Solina Accounts Oy | Professional & scientific | 2024 |
| Solun Elinvoima Oy | Other services | 2024 |
| Soma Kotka Oy | Other services | 2025 |
| Sonoco Finland Oy | Manufacturing | 1994 |
| Sorocaima Oy | Real estate | 2000 |
| Sosiaalipalvelut Elämän Avaimet Oy | Health & social care | 2024 |
| South Aid Freight Oy | Real estate | 2017 |
| South East Loading Oy | Transport & logistics | 2008 |
| Southeast Boat Service Oy | Wholesale & retail | 2021 |
| Southeast Marina Services Oy | Construction | 2018 |
| Spedition Services Finland Oy | Transport & logistics | 2005 |
| Stanoil Oy | Transport & logistics | 1993 |
| Steertec Ky | Professional & scientific | 1990 |
| Steveco Oy | Transport & logistics | 1987 |
| Still It Kommandiittiyhtiö | | 1990 |
| Storage & Handling Kotka Oy | Real estate | 2021 |
| Street Food Factory Oy | Hospitality | 2020 |
| Studio Ukkonen Oy | Professional & scientific | 2018 |
| Subha Spice Oy | Hospitality | 2026 |
| Suljennon Vesiosuuskunta | Water & waste | 2006 |
| Sulkama Oy | Construction | 2004 |
| Sulzer Pumps Finland Oy | Manufacturing | 2000 |
| Sunila Solutions Oy | Manufacturing | 2025 |
| Sunilan Kantola Oy | Real estate | 1988 |
| Suoda Oy | Professional & scientific | 2023 |
| Suomen Digitaalinen Tehdas Oy | Information & communication | 2023 |
| Suomen EU-Tähtitalot Oy | Wholesale & retail | 1997 |
| Suomen Kassayhtiö Oy | Information & communication | 2022 |
| Suomen Koulutusopisto Oy | Education | 2015 |
| Suomen Kuljetuspalvelu Oy | Other services | 2021 |
| Suomen Pohjavesilämmitys Oy | Construction | 2021 |
| Suomen Saaristoravintolat Oy | Hospitality | 2024 |
| Suomen Satamatekniikka Oy | Manufacturing | 2007 |
| Suomen Sportec Oy | Wholesale & retail | 1990 |
| Suomen Sähkömestarit Oy | Construction | 2025 |
| Suomen Turvallisuusopisto Oy | Education | 2013 |
| Suomen Uimaopetus Ky | Arts & recreation | 2013 |
| Suomen Varavoimatekniikka Oy | Wholesale & retail | 1995 |