| Seinäjoen Radiopojat Oy | Wholesale & retail | 1989 |
| Seinäjoen Rakennus ja Remontti Oy | Construction | 1998 |
| Seinäjoen Rakennusmaalaus Oy | Construction | 2004 |
| Seinäjoen Randewoo Oy | Wholesale & retail | 1993 |
| Seinäjoen Raskashuolto Oy | Other services | 2020 |
| Seinäjoen Rengaskeskus Oy | Wholesale & retail | 1989 |
| Seinäjoen Satoomo Oy | Real estate | 2007 |
| Seinäjoen Silmälasimarket Oy | Wholesale & retail | 1995 |
| Seinäjoen Sisustus Oy | Wholesale & retail | 1985 |
| Seinäjoen Squash ja Bowling Oy | Arts & recreation | 2013 |
| Seinäjoen Säiliöliikenne Oy | Transport & logistics | 2007 |
| Seinäjoen Talofixi Oy | Construction | 2025 |
| Seinäjoen Talonmiespalvelu Oy | Administrative & support | 2020 |
| Seinäjoen Talotimpurit Oy | Construction | 2005 |
| Seinäjoen Tangomarkkinat Oy | Arts & recreation | 1997 |
| Seinäjoen Tavara-Aitta Oy | Wholesale & retail | 1979 |
| Seinäjoen Tennistuki Oy | Arts & recreation | 1979 |
| Seinäjoen Teollisuussähkö Ky | Professional & scientific | 1987 |
| Seinäjoen Tevi-Mark Ky | Hospitality | 2001 |
| Seinäjoen Turva-Asennus OY | Administrative & support | 2013 |
| Seinäjoen Turvapalvelut Oy | Administrative & support | 1994 |
| Seinäjoen Työterveys Oy | Health & social care | 2016 |
| Seinäjoen Ulappa Oy | Real estate | 2021 |
| Seinäjoen VI-Tekniikka Oy | Construction | 1989 |
| Seinäjoen Varaosamyynti Oy | Real estate | 2011 |
| Seinäjoen Vesi- ja lämpöasennus avoin yhtiö | Construction | 2000 |
| Seinäjoen Yrityskiinteistöt Oy | Real estate | 2001 |
| Seinäjoen hautaus- ja juhlapalvelut Oy | Other services | 2017 |
| Seinäjoen ja Nurmon Kukka- ja Hautauspalvelu Oy | Wholesale & retail | 2016 |
| Seinäjoen kuntoutus Oy | Health & social care | 1980 |
| Seinäjoen liikuntakerho Oy | Education | 2024 |
| Seinäjoen opiskelijapalvelut Oy | Education | 2012 |
| Seinäjoki Activity Park Oy | Education | 2014 |
| Seinäjoki Areena Oy | Real estate | 1999 |
| Seinäjoki Festivals Oy | Arts & recreation | 2010 |
| Seinäjoki Squash Avoin yhtiö | Arts & recreation | 1992 |
| Seinäjoki Stadion Management Oy | Arts & recreation | 2011 |
| Seinäjoki Stadion Oy | Arts & recreation | 2015 |
| Seinäjokinet Oy | Information & communication | 2026 |
| Seipark Oy | Transport & logistics | 2010 |
| Seisa Oy | Real estate | 2005 |
| Seiverkot Oy | Energy | 2007 |
| Sekunnit ja tunnit Oy | Arts & recreation | 2021 |
| Selja Kodit Oy | Real estate | 2023 |
| Semio Oy | Professional & scientific | 2004 |
| Semko Oy | Manufacturing | 1995 |
| Seulakeus Oy | Construction | 2016 |
| Sevas Kodit Oy | Real estate | 1990 |
| Sevor Steel Oy | Manufacturing | 2024 |
| Shadow Capital Oy | Financial services | 2022 |
| ShadowSales Oy | Administrative & support | 2020 |
| Sib Homes Oy | Construction | 2022 |
| Sibvest Oy | Real estate | 2014 |
| Siipifarmi Oy | Agriculture & fishing | 1990 |
| Siivouspalvelu Hunnakko Oy | Administrative & support | 2022 |
| Sijoitusvirta Oy | Financial services | 2018 |
| Sijoitusyhtiö Hietakangas Oy | Real estate | 2020 |
| Sijoitusyhtiö Rintala Oy | Financial services | 1989 |
| Sikakangas Oy | Real estate | 2025 |
| Siljoo Oy | Wholesale & retail | 2022 |
| Silkkipaino Kari Niemi Ky | Manufacturing | 1980 |
| Silmäkonsultit Oy | Health & social care | 2025 |
| Simplynet Oy | Administrative & support | 2020 |
| Sinetiksi Visuals Oy | Professional & scientific | 2021 |
| Sinkosimot Oy | Financial services | 2013 |
| Sintesis Group Oy | Information & communication | 2023 |
| SippRik Oy | Wholesale & retail | 2012 |
| Sirkan Kenkä Ky | Wholesale & retail | 1973 |
| Sirrest Oy | Hospitality | 1994 |
| Sisam Invest Oy | Real estate | 1988 |
| Sisustussuunnittelu/Inredningsplanering Nina Mäkelä Ky | Professional & scientific | 2012 |
| Sisärakenne Topset Pohjanmaa Oy | Construction | 2014 |
| Skants Oy | Wholesale & retail | 2023 |
| Skin Seinäjoki Oy | Health & social care | 2026 |
| SkinMedic Oy | Health & social care | 2020 |
| Sky 9 Oy | Wholesale & retail | 2016 |
| Smarter Solutions Oy | Professional & scientific | 2024 |
| Smile-Invest Oy | Real estate | 1983 |
| Sofica Oy | Information & communication | 2009 |
| Sofram Kebab & Pizzeria Oy | Hospitality | 2005 |
| Softacon Finland Oy | Information & communication | 2008 |
| Sohovi Oy | Wholesale & retail | 2021 |
| Soinin Maalauspalvelu Ky | Construction | 2010 |
| Soukkakuljetus oy | Transport & logistics | 2025 |
| Soundbros Oy | Wholesale & retail | 2007 |
| Sovintotalous Oy | Public administration | 2026 |
| Spices Chef Oy | Wholesale & retail | 2017 |
| Sponsio Oy | Construction | 2001 |
| Stable Rosette Oy | Agriculture & fishing | 2024 |
| Staff Port Oy | Information & communication | 1985 |
| StepWorks Oy | Manufacturing | 2026 |
| Steplong Oy | Administrative & support | 1989 |
| Stonesto Oy | Financial services | 2022 |
| Storm's Wood Oy | Wholesale & retail | 2021 |
| Studio Amfora Ky | Manufacturing | 1985 |
| Studio Good Vibes Oy | Arts & recreation | 2023 |
| Studio LadyLike Oy | Arts & recreation | 2009 |
| Studio Murros Oy | Health & social care | 2018 |
| Su-Ju-Sijoitus Oy | Wholesale & retail | 1991 |
| Subcom Oy | Hospitality | 2006 |