| Oy SFA-Consulting-Marketing Group Ltd | Muurame | 2005 |
| Oy SHH Academic Business Consulting Ab | Helsinki | 1995 |
| Oy SK-Reviisorit Ab | Seinäjoki | 2009 |
| Oy SLX Housing Ltd | Lahti | 2015 |
| Oy SNE Environment Engineering Ltd | Seinäjoki | 1992 |
| Oy SNY ThePlan Ab | Espoo | 2014 |
| Oy SS-Finance Ab | Kesälahti | 1999 |
| Oy Sahia Consulting Ltd | Espoo | 2005 |
| Oy Salexport Ab | Lapua | 2018 |
| Oy Samppa Lajunen Ltd | Jyväskylä | 2003 |
| Oy Sandaco Ab | Karperö | 2023 |
| Oy Sanil Europe Ltd | Helsinki | 1995 |
| Oy Santa Claus Licensing Ltd | Helsinki | 2000 |
| Oy Sauloner Ltd | Kuopio | 2008 |
| Oy Saunawise Ltd | Forssa | 2019 |
| Oy Scan Fibre Ltd | Imatra | 1990 |
| Oy ScanShow Ab | Espoo | 2008 |
| Oy Scanboni Ab | Helsinki | 1993 |
| Oy Scandia Protech Ltd | Lappeenranta | 2007 |
| Oy Scandinavian Search & Recruitment Ab | Turku | 1998 |
| Oy Scandinavian Show House Ltd | Seinäjoki | 1995 |
| Oy Schapeau Ab | Helsinki | 2026 |
| Oy Schedule Ab | Helsinki | 1990 |
| Oy Schmalz Ab | Vantaa | 2006 |
| Oy Sebwil Ab | Söderkulla | 2010 |
| Oy SecGen Ltd | Helsinki | 2007 |
| Oy SecVeto Ab | Espoo | 2014 |
| Oy Secure-Consulting Ab | Vöyri | 1990 |
| Oy Separation Research Ab | Turku | 1976 |
| Oy Sercoma Ab | Parainen | 2005 |
| Oy Seres Ab | Vaasa | 2008 |
| Oy ServicePulse Ab | Pietarsaari | 2024 |
| Oy Sesla Ltd | Hamina | 2008 |
| Oy Sethonian Ab | Helsinki | 2013 |
| Oy Shinbo Ab | Kirkkonummi | 1986 |
| Oy Shippro Ltd | Masku | 1986 |
| Oy Shiptech Ab | Helsinki | 2010 |
| Oy Shock Recycling Solutions Ltd. | Oulu | 2020 |
| Oy Sifterium Ltd | Helsinki | 2002 |
| Oy Sigma Ab | Helsinki | 1953 |
| Oy Silva Invest Ab | Helsinki | 1984 |
| Oy Simplex Engineering Ltd | Vantaa | 2007 |
| Oy SimplySoft Ab | Pietarsaari | 2021 |
| Oy Sirius Capital Partners Ab | Helsinki | 2014 |
| Oy Sirra Ab | Jorvas | 2010 |
| Oy Site Logic Ab | Helsinki | 2005 |
| Oy Sjökulla Ab | Tammisaari | 1963 |
| Oy Skeye Ab | Helsinki | 1990 |
| Oy SloboCon Ltd | Espoo | 2010 |
| Oy Snellco Ab | Lahti | 2024 |
| Oy Soft Protector Ltd. | Espoo | 1991 |
| Oy Soinio & Co | Turku | 2000 |
| Oy Solve Ab | Vantaa | 1995 |
| Oy Solventia Ab | Espoo | 2011 |
| Oy Solvik International Ab | Tampere | 1993 |
| Oy Solvit Ab | Helsinki | 2001 |
| Oy Sophie-International Ab | Helsinki | 1994 |
| Oy Soul-Productions Finland Ltd | Helsinki | 1997 |
| Oy Speakers Forum Finland Ab | Espoo | 1998 |
| Oy Spectrinal Ab | Vantaa | 1997 |
| Oy Spectrum Investments Ltd | Kangasala | 1993 |
| Oy Spiritus Historiae Ab | Helsinki | 1989 |
| Oy Sport Management Finland Ltd | Vaajakoski | 2010 |
| Oy Sportmark Martin & Martin Ab | Turku | 1992 |
| Oy Stablehouse Ab | Hollola | 2008 |
| Oy Stahanov Ab | Helsinki | 1990 |
| Oy Star Communications Ab | Vaasa | 2026 |
| Oy Steelpro Ltd | Vantaa | 1997 |
| Oy Stellaria Media Ab | Helsinki | 1997 |
| Oy Stellio Ab | Kauniainen | 2014 |
| Oy Stenström Engineering Ab | Porvoo | 2019 |
| Oy Stimulator Ab | Helsinki | 1989 |
| Oy Stone and Roses Ltd | Kullaa | 2004 |
| Oy Stop Noise Finland Ltd | Jyväskylä | 1995 |
| Oy Storby structural Ab | Kuusisto | 2004 |
| Oy Storvest Ab | Pietarsaari | 2012 |
| Oy Straightlines Corporation | Söderkulla | 2005 |
| Oy Strand Kapital Ab | Seinäjoki | 2015 |
| Oy Stratamax Ab | Helsinki | 1993 |
| Oy Strateg - Loyalty Finland Ab | Porvoo | 2003 |
| Oy Stratotec Ab | Koskenkylän Saha | 2007 |
| Oy Stretta Artists Management Ltd | Järvenpää | 1990 |
| Oy Strongwell Ab | Helsinki | 1989 |
| Oy Strumpa & Lång Ab | Hämeenlinna | 2021 |
| Oy Stråhlmann Yacht Design Ab | Porvoo | 2007 |
| Oy Strömsholm Ab | Inkoo | 2022 |
| Oy Strömsö Business Consulting Ab | Vaasa | 2022 |
| Oy Studio Charlotta Boucht Ab | Helsinki | 1997 |
| Oy Studio Fotocenter Ab | Vaasa | 1986 |
| Oy Studio Gaston Ab | Askola | 1979 |
| Oy Studio L & B Ab | Helsinki | 2008 |
| Oy Studio Lindberg Ab | Kärrby | 1988 |
| Oy Studio Lindh Ab | Espoo | 1977 |
| Oy Studio Lumo Ab | Valko | 1989 |
| Oy Studio Nevanlinna Ab | Kauniainen | 1980 |
| Oy Succee Ab | Pori | 2007 |
| Oy Sundman Consulting Ab | Helsinki | 1962 |
| Oy Sunny Capital inc. | Jyväskylä | 1990 |
| Oy Sunsec Ab | Mäntsälä | 1996 |
| Oy Suomen Hilaris Ab | Helsinki | 1995 |