| Shaun Williams Property Renovations Ltd | Manufacturing | 2024 |
| Shearwater Eco Ltd | Manufacturing | 2018 |
| Shineaway Carwash Ltd | Administrative & support | 2024 |
| Shop Holistic Limited | Wholesale & retail | 2015 |
| Shosha Barber Ltd | Other services | 2025 |
| Shutterhaus Ltd | Wholesale & retail | 2025 |
| SIB Solutions Limited | Construction | 2014 |
| Signature Factory Ltd | Hospitality | 2023 |
| Signtune Limited | | 1953 |
| Signum-Health Ltd | Information & communication | 2016 |
| Silk RD IP Holding Limited | Financial services | 2025 |
| Simone Angel Care Limited | Health & social care | 2024 |
| Simpletel Limited | Information & communication | 2017 |
| Simply DO Ideas Limited | Information & communication | 2015 |
| Simply Factoring Brokers Ltd | Financial services | 2009 |
| Sindher Heritage Ltd | Real estate | 2025 |
| SIR Alfred Cars Limited | Wholesale & retail | 2017 |
| Sister Sioux Vintage Ltd | Wholesale & retail | 2024 |
| SK Auto Care Ltd | Other services | 2025 |
| SK Grewal Limited | Wholesale & retail | 2024 |
| Skeldify Ltd | Construction | 2025 |
| Sky Life Accountancy Limited | Professional & scientific | 2018 |
| Slater & Morgan Property Limited | Real estate | 2021 |
| SLE Properties Limited | Construction | 2024 |
| SLG Coaching Ltd | Health & social care | 2025 |
| SLH Bar Company Limited | Hospitality | 2016 |
| Smartpotz Ltd | Wholesale & retail | 2013 |
| Smartups Consultancy Ltd | Information & communication | 2023 |
| Smartze Limited | Information & communication | 2013 |
| SMC Bathrooms & Kitchens Ltd | Other services | 2019 |
| SMC Boiler Repair and Care Ltd | Construction | 2023 |
| Smikle Investments Ltd | Real estate | 2022 |
| Smoothmoove Conveyancing Limited | Professional & scientific | 2025 |
| Snail BOY Limited | Financial services | 2025 |
| SNC Programming Ltd | Arts & recreation | 2026 |
| Sneggy Chippy Ltd | Hospitality | 2023 |
| Snowden Family Holidays Ltd | Administrative & support | 2026 |
| SO Coffee Trades Ltd | Other services | 2017 |
| Softnsafe Ltd | Wholesale & retail | 2010 |
| Solar Pavilion Construction Limited | Construction | 2025 |
| Solarheat Limited | Construction | 2026 |
| Solix Marketing Ltd | Professional & scientific | 2026 |
| Solvit Systems Ltd | Manufacturing | 2014 |
| Solvitall Limited | Other services | 2010 |
| Sort My Site Limited | Information & communication | 2026 |
| Sound Inspection Limited | Professional & scientific | 2003 |
| South Wales Accounting Services Ltd | Professional & scientific | 2018 |
| South Wales Cleaning Company Limited | Administrative & support | 2025 |
| South Wales Electrical & Property Ltd | Construction | 2024 |
| South Wales Knee Clinic Ltd | Health & social care | 2014 |
| South Wales Mobility Limited | Manufacturing | 2015 |
| South Wales Monuments Limited | Manufacturing | 1988 |
| South Wales Property Developers Ltd | Construction | 2020 |
| South Wales Property Group Limited | Real estate | 2024 |
| South Wales Service Centre Limited | Wholesale & retail | 2011 |
| South Wales Sleeper Supplies Limited | Wholesale & retail | 2015 |
| South Wales Tyre Centre Ltd | Wholesale & retail | 2021 |
| SP Carpentry Services Ltd | Construction | 2016 |
| SP33DY Parcels Ltd | Transport & logistics | 2024 |
| Sparey Construction Ltd | Construction | 2022 |
| Sparticulate Ltd | Other services | 2015 |
| Speak Visually Ltd | Professional & scientific | 2025 |
| Spearhead Property Maintenance Limited | Construction | 2025 |
| Specialist Precast Products Limited | Extraterritorial | 2009 |
| Speedfast Tool Hire Limited | Administrative & support | 2017 |
| Splash Studios Ltd | Arts & recreation | 2023 |
| SPM Heating & Air Conditioning Services Ltd. | Extraterritorial | 2013 |
| Sporting Records Online Ltd | Information & communication | 2017 |
| Sporttape Limited | Wholesale & retail | 2010 |
| Spotnails (Holdings) Limited | Financial services | 2018 |
| Spotnails Limited | Wholesale & retail | 1995 |
| Spotnails Maestri Limited | Wholesale & retail | 2019 |
| Sprinkler Industry Training Academy Limited | Education | 2021 |
| SQL Star Limited | Professional & scientific | 2015 |
| SR Caerphilly Ltd | Hospitality | 2023 |
| Srus Ltd | Wholesale & retail | 2003 |
| ST Davids Homes Ltd | Construction | 2016 |
| St.Ilan Ltd | Wholesale & retail | 2000 |
| Starlight Electrical Services (South Wales) Limited | Construction | 2012 |
| Starline Awnings & Blinds Limited | Manufacturing | 2007 |
| Steelee Door Services Limited | Administrative & support | 2016 |
| Stempowered Learning Ltd | Education | 2017 |
| Stephen Harding Limited | Transport & logistics | 2017 |
| Stephen Morris Management Limited | Professional & scientific | 2017 |
| Steve H C Business Accounts Limited | Professional & scientific | 2008 |
| Stonecroft Property Company Ltd | Real estate | 2026 |
| Stonerite Ltd | Manufacturing | 2007 |
| Stonerite Trading Limited | Manufacturing | 2026 |
| Storeradar Limited | Information & communication | 2024 |
| Street & Co Property Developments Ltd | Construction | 2025 |
| Stronghold Cleaning Services Ltd | Extraterritorial | 2025 |
| Styles Electrical Limited | Construction | 2005 |
| Su-Med International (UK) Limited | Manufacturing | 1985 |
| Summit Safety Ltd | Professional & scientific | 2025 |
| Summum X Ltd | Financial services | 2025 |
| Sumo Couriers Ltd | Transport & logistics | 2025 |
| Sunflower Food Ltd | Hospitality | 2025 |
| Sunny Property Ltd | Real estate | 2016 |
| Sunnybank Equestrian Centre Ltd | Arts & recreation | 2025 |
| Superamped Ltd | Information & communication | 2023 |