| Sofidel UK Limited | Manufacturing | 1988 |
| Soft-Tec Controls Limited | Information & communication | 2013 |
| Solar Direct Ltd | Construction | 2025 |
| Sole Takers Limited | Extraterritorial | 2025 |
| Soleo Property Ltd | Real estate | 2024 |
| Sorayas Neath Ltd | Wholesale & retail | 2019 |
| South Valley Travel Co. Limited | Administrative & support | 2025 |
| South Wales Fork Trucks Hire Limited | Administrative & support | 2007 |
| South Wales Medical Services Limited | Health & social care | 2022 |
| South Wales Plant Sales Limited | Extraterritorial | 2022 |
| South Wales Renewables Limited | Construction | 2024 |
| South Wales Snagging Co Ltd | Professional & scientific | 2026 |
| South Wales Sofas Limited | Wholesale & retail | 2025 |
| South West UK Roofing Limited | Construction | 2026 |
| South Western Roofing Limited | Construction | 2023 |
| SP & AM Building Services Ltd | Construction | 2017 |
| Spacewoman Ltd | Wholesale & retail | 2024 |
| Spanner Monkey Garage Ltd | Wholesale & retail | 2024 |
| Spareys CNC Machining Services Limited | Professional & scientific | 2013 |
| Sparky Academy Ltd | Education | 2022 |
| Spartan Waste and Tree Services Ltd | Water & waste | 2026 |
| Sparticle UK Limited | Hospitality | 2017 |
| Special Assignments Ltd | Administrative & support | 2006 |
| Special Branch Tree Services Limited | Agriculture & fishing | 2024 |
| Specialist Business Solutions Ltd. | Professional & scientific | 2009 |
| Speciality Carbons Limited | Mining & quarrying | 2003 |
| Spectra Asset Integrity Management Limited | Administrative & support | 2015 |
| Spectrum TV C.I.C. | Information & communication | 2019 |
| Spectrum Wide Community Interest Company | Professional & scientific | 2024 |
| Spencer John Holdings Ltd | Financial services | 2025 |
| Spice IS Nice Ltd | Hospitality | 2023 |
| Spiel Productions Limited | Professional & scientific | 2011 |
| Spiral Horizons CIC | Administrative & support | 2025 |
| Split Hero Limited | Information & communication | 2018 |
| Sportec Embroidery & Printing Limited | Manufacturing | 2010 |
| Sportsviz Limited | Information & communication | 2012 |
| Spot on Cleaning Supplies Limited | Wholesale & retail | 2011 |
| Spray Tech Roads Limited | Construction | 1999 |
| Spud Hub Neath Ltd | Hospitality | 2025 |
| Squatch IT Ltd | Wholesale & retail | 2025 |
| SRA Haulage Ltd | Transport & logistics | 2026 |
| Srcc Stores Limited | Wholesale & retail | 2015 |
| SRW Carpentry Limited | Manufacturing | 2024 |
| SS Cleaning Solutions Wales Limited | Administrative & support | 2025 |
| SS Residential Lettings Limited | Real estate | 2009 |
| SS1 Denticare Ltd | Health & social care | 2025 |
| SSB Competitive Cars Ltd | Wholesale & retail | 2025 |
| ST Cash and Carry Ltd | Wholesale & retail | 2026 |
| ST Davids Holdings Limited | Real estate | 2007 |
| ST Food and Wine Ltd | Wholesale & retail | 2019 |
| ST Martin's Associates Ltd | Professional & scientific | 2022 |
| ST. Michaels Property Development and Investments Limited | Real estate | 2016 |
| Steel Town Motors Ltd | Wholesale & retail | 2024 |
| Steele Mcneil Ltd | Financial services | 2021 |
| Steelman Exterior Cleaning Solutions Ltd | Administrative & support | 2026 |
| Stella Retail Ltd | Wholesale & retail | 2021 |
| Stephen Cocks Motorcycle Training Limited | Education | 2025 |
| Steve Gorvett Maintenance Limited | Administrative & support | 2014 |
| Steve Powell Limited | Administrative & support | 2003 |
| STG Design Ltd | Professional & scientific | 2024 |
| Stokes Trading (GB) Ltd | Wholesale & retail | 2025 |
| Stone Tafarns Limited | Hospitality | 2022 |
| Stratsync Limited | Information & communication | 2026 |
| Strinatipubs Ltd | Hospitality | 2024 |
| Stronger United Ltd | Education | 2016 |
| Studio Unbranded Limited | Other services | 2013 |
| Sugar Rush Neath Ltd | Wholesale & retail | 2021 |
| Suitegood Limited | Manufacturing | 1994 |
| Summers Country Estates Ltd | Real estate | 1990 |
| Sunethra Ltd | Health & social care | 2014 |
| Sunshine Home Improvements Limited | Construction | 2012 |
| Supreme NG Ltd | Hospitality | 2019 |
| Supreme Timberframe Ltd | Construction | 2019 |
| Sureserve Energy Services Wales Limited | Construction | 2014 |
| Surviva Ltd | Manufacturing | 2009 |
| Sustainable Industries Ltd | Professional & scientific | 2024 |
| Sustainable Site Power Ltd | Energy | 2019 |
| SW Energy Consultants Ltd | Professional & scientific | 2026 |
| SW Waste Management Ltd | Water & waste | 2021 |
| Swan Programming Limited | Professional & scientific | 2024 |
| Swansea Bulk Handling Limited | Transport & logistics | 2007 |
| Swansea Gastroenterology Ltd | Health & social care | 2021 |
| Swansea Motor Vehicle Sales Limited | Wholesale & retail | 1995 |
| Swansea Rentals Ltd | Real estate | 2025 |
| Swansea Valley Asset Management Ltd | Administrative & support | 2020 |
| Swansea Valley Tarmacadam Ltd | Construction | 2015 |
| Swedish Makers Ltd | Wholesale & retail | 2024 |
| Swift Property Care Limited | Administrative & support | 2009 |
| Swiftfulfill Ltd | Wholesale & retail | 2024 |
| Swn-Yr-Afon Developments Ltd | Construction | 2020 |
| Symbiosis Solutions Ltd | Transport & logistics | 2020 |
| Synergy Sales Partner Limited | Professional & scientific | 2025 |
| Systems Approach Ltd | Professional & scientific | 2023 |
| SŴN Sounds Music Ltd | Arts & recreation | 2023 |
| T Deck Safety Systems Ltd | Construction | 2021 |
| T H W Entertainment Ltd | Hospitality | 2018 |
| T J Landscapes Services Ltd | Administrative & support | 2021 |
| T Michael Associates Limited | Administrative & support | 2012 |
| T Recycle Ltd | Construction | 2020 |
| T&E Home Properties Ltd | Real estate | 2025 |