| Sophia ANN Healthcare Ltd | Health & social care | 2022 |
| Sophie Collins Photography Ltd | Professional & scientific | 2025 |
| Soraderm Ltd | Wholesale & retail | 2025 |
| Soraderma Ltd | Wholesale & retail | 2025 |
| Soulbaytech Ltd | Wholesale & retail | 2024 |
| Sound Sync Limited | Administrative & support | 2022 |
| South East Wales Rivers Trust | Agriculture & fishing | 2007 |
| South Wales Capital Holdings Ltd | Financial services | 2026 |
| South Wales Marketing Limited | Professional & scientific | 2012 |
| South Wales One CIC | Information & communication | 2024 |
| South Wales Safety Ltd | Professional & scientific | 2024 |
| South Wales Security Limited | Administrative & support | 2023 |
| South Wales Windows Ltd | Construction | 2018 |
| Sovereign Traders Limited | Wholesale & retail | 2019 |
| Sowe Global Ltd | Wholesale & retail | 2025 |
| SP Mirror Wardrobes Ltd. | Manufacturing | 2015 |
| Spargo's Chilli JAM Limited | Manufacturing | 2021 |
| Spartan Outdoors Limited | Wholesale & retail | 2026 |
| Spartan Sprinkler Installations Ltd | Construction | 2021 |
| Spartanbank Limited | Administrative & support | 2008 |
| Spectrum Construction Services Ltd | Construction | 2019 |
| Spectrum Property Developments Ltd | Real estate | 2025 |
| Speed Strip Limited | Professional & scientific | 1999 |
| Speedlink Freight Limited | Transport & logistics | 2003 |
| Spencer and Evie Homes Limited | Real estate | 2021 |
| Spic & Span Pro Cleaning Ltd | Administrative & support | 2023 |
| Spice Pontypridd Ltd | Hospitality | 2016 |
| Spozer UK Ltd | Wholesale & retail | 2021 |
| Springdoor Limited | Education | 2005 |
| Springfield Kennels Limited | Other services | 2012 |
| SPRINKLERS360 Holdings Limited | Financial services | 2023 |
| SPRINKLERS360 Ltd | Construction | 2018 |
| Squadr Ltd | Information & communication | 2026 |
| Squirrel Collectables Limited | Wholesale & retail | 2018 |
| SR Recoverys Limited | Transport & logistics | 2025 |
| SRM Clinics Ltd | Health & social care | 2026 |
| ST Anns Care Limited | Financial services | 2025 |
| ST. Anne's Nursing Home Limited | Health & social care | 1945 |
| Stamina Delivery Logistics Ltd | Transport & logistics | 2020 |
| Stan Integrated Services Limited | Construction | 2026 |
| Staples Drylining Limited | Construction | 2018 |
| Star Turtle Ltd | Arts & recreation | 2002 |
| Star-Stuff Science Academy Ltd | Education | 2025 |
| Starlink Electrical Limited | Construction | 2021 |
| Startrite Nurseries Limited | Administrative & support | 2000 |
| Startupsauce Ltd | Professional & scientific | 2019 |
| Steadler Construction Limited | Construction | 2025 |
| Steadler Consulting Limited | Professional & scientific | 2024 |
| Steadler Group Limited | Construction | 2023 |
| Steele Construction Limited | Construction | 2011 |
| Stellar Fitout Contractors Ltd | Construction | 2013 |
| Stellarcart Technologies Ltd | Wholesale & retail | 2025 |
| Stelway Trading Co., Ltd | Wholesale & retail | 2025 |
| Stephen's Bakery Limited | Wholesale & retail | 2015 |
| Sterakalin Ltd | Wholesale & retail | 2026 |
| Stevenson Design Engineering Ltd | Professional & scientific | 2017 |
| Stevie LEW Design Ltd | Professional & scientific | 2022 |
| Stiwdio 37 CIC | Wholesale & retail | 2023 |
| Stoneage Construction Ltd | Construction | 2024 |
| Stonebridge Cornerstone Consulting Ltd | Professional & scientific | 2017 |
| Stonecraft Group Limited | Financial services | 2026 |
| Stonecraft Paving and Driveways Limited | Construction | 2026 |
| Stonecraft Paving Ltd | Administrative & support | 2025 |
| Stoneman Brown & Davies Developments Limited | Construction | 2019 |
| Storage Management Services UK Ltd | Construction | 2021 |
| Stradling Holdings Limited | Administrative & support | 2007 |
| Stradling Tax Services Limited | Professional & scientific | 1995 |
| Stray Clothing Ltd | Wholesale & retail | 2021 |
| String Sky Monkey Ltd | Wholesale & retail | 2024 |
| Stronghold Scaffold Limited | Construction | 2026 |
| Stuart Lock Consulting Limited | Administrative & support | 2016 |
| Stuart Richardson Consultancy Ltd | Construction | 2026 |
| Study South Wales Limited | Education | 2022 |
| Sullivans Business Consultancy Limited | Information & communication | 2011 |
| Summit Civils and Arboriculture Limited | Construction | 2025 |
| Summit Projects Solutions Ltd | Construction | 2025 |
| Sunset Sports Limited | Wholesale & retail | 2002 |
| Superstar Group Co., Ltd | Wholesale & retail | 2024 |
| Supply Only Bedrooms Ltd | Wholesale & retail | 2008 |
| Suprent Pro UK Ltd | Wholesale & retail | 2024 |
| Sure 2 Shine Ltd | Administrative & support | 2024 |
| Sureplan Wills and Estates Ltd | Financial services | 2025 |
| Sureshine 2 Ltd | Administrative & support | 2025 |
| Sureshine Window Cleaning Limited | Administrative & support | 2002 |
| Swansea DC Ltd | Health & social care | 2025 |
| Swiftheat UK Group Ltd | Construction | 2025 |
| SWV 18HS Limited | Construction | 2020 |
| SWV 5HS Limited | Construction | 2020 |
| Sycamore Construction Group Ltd | Construction | 2016 |
| Sycamore Tree Properties Limited | Real estate | 2025 |
| Synrad Ltd | Manufacturing | 2023 |
| Sysdemics Ltd | Education | 2026 |
| Systems Paradigm Limited | Information & communication | 2015 |
| T Britton Construction Limited | Construction | 2023 |
| T John Transport Limited | Transport & logistics | 2010 |
| T Property Services & Management Ltd | Real estate | 2019 |
| T-House Ltd | Wholesale & retail | 2025 |
| T3 Project Management & Delivery Ltd | Construction | 2022 |
| TAF DC Ltd | Health & social care | 2023 |
| Tafarn YN Y Coed Ltd | Hospitality | 2025 |