| Satakunnan Teleurakointi Oy | Construction | 2010 |
| Satakunnan Teollisuus- ja Siivouspalvelut Oy | Administrative & support | 2011 |
| Satakunnan Teollisuuspalvelu Oy | Real estate | 2006 |
| Satakunnan Terveyspalvelu Oy | Health & social care | 1995 |
| Satakunnan Tilinpito Oy | Professional & scientific | 2011 |
| Satakunnan Tilipalvelu Oy | Professional & scientific | 1992 |
| Satakunnan Turvatekniikka Oy | Administrative & support | 2017 |
| Satakunnan Vesilämpötalo Ky | Construction | 2006 |
| Satakunnan Viherpalvelu Oy | Administrative & support | 1987 |
| Satakunnan Vuokratilat Oy | Real estate | 2020 |
| Satakunnan YH-Rakennuttaja Oy | Real estate | 1986 |
| Satakunnan Yrittäjämedia Oy | Professional & scientific | 2010 |
| Satakunnan Yritystili Oy | Professional & scientific | 1991 |
| Satakunnan ammattikorkeakoulu Oy | Education | 2011 |
| Satakunnan auto-ja rengaspalvelu Oy | Other services | 2025 |
| Satakunnan kalustemiehet Oy | Construction | 2009 |
| Satakunnan terveys- ja hyvinvointicenter Oy | Health & social care | 2004 |
| Satakunnan tukihenkilöpalvelut Oy | Health & social care | 2018 |
| Satakunnan Ässäputki Oy | Construction | 2007 |
| Satakymppi Group Oy | Wholesale & retail | 1988 |
| Satalaskenta Oy | Professional & scientific | 1978 |
| Satamaalaus Oy | Construction | 2025 |
| Satametalli Oy | Manufacturing | 1993 |
| Satamuutto Oy | Transport & logistics | 2021 |
| Sataneule Oy | Manufacturing | 1957 |
| Satanuohous Oy | Administrative & support | 2023 |
| Sataosaajat Osuuskunta | Administrative & support | 1995 |
| Satapaine Oy | Manufacturing | 2013 |
| Satapori Oy | Wholesale & retail | 2009 |
| Satapower Oy | Construction | 2022 |
| Sataputki Oy | Manufacturing | 1992 |
| Sataraudoitus Oy | Construction | 2019 |
| Sataravinne Ky | Wholesale & retail | 2015 |
| Satarengas Oy | Wholesale & retail | 2026 |
| Satasata Oy | Construction | 1990 |
| Satasteel Oy | Manufacturing | 1991 |
| Sataterapia Oy | Health & social care | 2019 |
| Satatuisku Oy | Real estate | 2013 |
| Satatukku Oy | Wholesale & retail | 2013 |
| Satatyö Oy | Construction | 1992 |
| Satoco Oy | Hospitality | 2016 |
| Saunatontut Oy | Real estate | 2006 |
| Scan-Mikael Oy | Manufacturing | 2001 |
| Scandi-Alloys Oy | Wholesale & retail | 1983 |
| Scandinavian Pro Cosmetics Oy Ab | Wholesale & retail | 2015 |
| Scanpiping Oy | Manufacturing | 2019 |
| Seaport Services Pori Oy | Transport & logistics | 2023 |
| Seasons HR Management Oy | Administrative & support | 2011 |
| Second Line Oy | Arts & recreation | 1993 |
| Sectilat Oy | Real estate | 2012 |
| Sehaia Oy | Arts & recreation | 2020 |
| Seinäjoen kukka- ja hautauspalvelu oy | Other services | 2024 |
| Selin Pojat Avoinyhtiö | Hospitality | 2016 |
| Semecaro Oy | Real estate | 2008 |
| Seppo Rantanen Oy | Education | 1996 |
| Seppä-Kuuri Oy | Other services | 2021 |
| Seretel OÜ, sivuliike Suomessa | Construction | 2021 |
| Servio Oy | Professional & scientific | 2020 |
| Setari Ky | Wholesale & retail | 1988 |
| Setälä Engineering Oy | Professional & scientific | 2016 |
| Seven Invest Oy | Financial services | 2026 |
| Shaman capitals Oy | Professional & scientific | 2023 |
| Shanora International Oy | Wholesale & retail | 2025 |
| Shedfish Oy | Agriculture & fishing | 2011 |
| Shengli Oy | Hospitality | 2017 |
| Shg Emmi Etolin Oy | Health & social care | 2026 |
| Shivakripa Oy | Hospitality | 2022 |
| Shop Piama Ky | Wholesale & retail | 1999 |
| Shuffle Pori Oy | Arts & recreation | 2025 |
| Siam ravintolat oy | Hospitality | 2024 |
| Sidahl Oy | Health & social care | 1999 |
| Sidekicks C Drops Oy | Administrative & support | 2020 |
| Signal Pori Avoin Yhtiö | Information & communication | 1992 |
| Siikaranta Camping avoin yhtiö | Hospitality | 2018 |
| Siipyyntien vesiosuuskunta - Sidebyvägens vattenandelslag | Water & waste | 2015 |
| Siirtolaite Ky Tapani Kujansuu | Wholesale & retail | 1995 |
| Siirtosäkitys Oy | Transport & logistics | 2004 |
| Siivouspalvelu Suomi Ky | Administrative & support | 2013 |
| Siivouspalvelu T.Saarinen Oy | Administrative & support | 1991 |
| Siivouspori Oy | Administrative & support | 1999 |
| Sijoitukset E Laine Oy | Construction | 1989 |
| Sijoitusrinki Oy | Real estate | 2022 |
| Sikuriina Oy, Lastensuojelun avopalvelut | Health & social care | 2019 |
| Silpax Oy | Construction | 2005 |
| Silta Advisors Group Oy | Professional & scientific | 2025 |
| Simo Laakso Kommandiittiyhtiö | Wholesale & retail | 1985 |
| Sinettiduo avoin yhtiö | Agriculture & fishing | 2024 |
| Sini-Tiimi Oy | Manufacturing | 1992 |
| Sinnis Services Oy | Manufacturing | 2011 |
| Sirke Suni Oy | Other services | 2022 |
| Sirkustorin Lounas Ky | Hospitality | 1991 |
| Sis&Bro Oy | Other services | 2014 |
| Sisustus Mokka Oy | Wholesale & retail | 2009 |
| Sisustus Sininen Aitta Oy | Wholesale & retail | 2015 |
| Sisustusliike Amalia Ky | Construction | 2009 |
| Sitku Oy | Professional & scientific | 2004 |
| Sivuhonka Oy | Manufacturing | 1984 |
| Sixth Part Oy | Hospitality | 2015 |
| Sjöbergin Liiketilat Oy | Real estate | 1989 |
| Sjöbergson & Co Ab | Financial services | 2025 |