| SQG Stores Ltd | Wholesale & retail | 2025 |
| SQI (Gower) Ltd | Professional & scientific | 2023 |
| Square on Ltd | Construction | 2024 |
| Square PEG Investments Limited | Real estate | 2003 |
| Squire Court Management Company Limited | Other services | 1984 |
| Squire Court Properties Limited | Households | 2013 |
| Squirrel Walk 1968 Limited | Extraterritorial | 2014 |
| SR Hospitality Limited | Hospitality | 2025 |
| SR Williams Plumbing and Heating Ltd | Construction | 2025 |
| Srbj Ltd | Agriculture & fishing | 2022 |
| SRD Properties Limited | Real estate | 2006 |
| Sree IT Solutions Ltd | Information & communication | 2024 |
| SRI Varaki Ltd | Real estate | 2025 |
| SRJ Lofts & Renovations Ltd | Construction | 2025 |
| SRS Innovation Ltd | Professional & scientific | 2015 |
| SS Cafe Bar Limited | Hospitality | 2023 |
| SS TEC Limited | Information & communication | 2019 |
| SSC Pecs Limited | Construction | 2025 |
| SSD Management Ltd | Professional & scientific | 2015 |
| Ssdn Health Care Ltd | Health & social care | 2024 |
| Ssmr Limited | Hospitality | 2024 |
| SSR Property Developments Ltd | Real estate | 2025 |
| SSS Home Improvements Ltd | Construction | 2025 |
| ST Brides Broad Haven Limited | Households | 2009 |
| ST Construction Europe Ltd | Construction | 2023 |
| ST Georges Home Care Ltd | Health & social care | 2015 |
| ST Giles Analytics Ltd | Professional & scientific | 2018 |
| ST Giles London Ltd | Administrative & support | 2017 |
| ST Helen's Vape Shop Limited | Wholesale & retail | 2026 |
| ST Helens (Swansea) Management Limited | Households | 2008 |
| ST James Funeral Home Ltd | Other services | 2021 |
| ST James Veterinary Group Limited | Professional & scientific | 2018 |
| ST Leger Crescent Limited | Households | 1995 |
| ST Madoc Christian Youth Camp | Hospitality | 2006 |
| ST Mary's Square Developments Limited | Real estate | 2015 |
| ST Mary's Street Limited | Real estate | 2015 |
| ST Teilo's (Pontarddulais) LLP | | 2020 |
| ST. Annes Mumbles Management Limited | Real estate | 2007 |
| Stack of Clubs Limited | Hospitality | 2018 |
| Stag Beer & Bucks Ltd | Hospitality | 2025 |
| Stag Estates Limited | Real estate | 1972 |
| Stag Hire Limited | Administrative & support | 2020 |
| Stageskool Theatre Arts Ltd | Education | 2020 |
| Stagewell Ltd | Extraterritorial | 2015 |
| Stainlessclad UK Ltd | Manufacturing | 2017 |
| Stalanowski Family Real Estate Ltd | Real estate | 2022 |
| Stampa Communications Limited | Professional & scientific | 2012 |
| Standard Consultancy Services Limited | Wholesale & retail | 2022 |
| Standout Capital Solutions Ltd | Financial services | 2022 |
| Standout Professional Services Ltd | Professional & scientific | 2026 |
| Stanson Properties Ltd | Real estate | 2024 |
| Star Abode Limited | Real estate | 2017 |
| Star Cash and Carry Swansea Ltd | Wholesale & retail | 2026 |
| Star Gaming Ltd | Information & communication | 2023 |
| Star GAS Services Wales Limited | Construction | 2023 |
| Star Savouries Limited | | 1987 |
| Star Transport B'Ham Ltd | Transport & logistics | 2017 |
| Star Tuition South Wales Limited | Education | 2022 |
| Star Walk (Wales) Limited | Administrative & support | 2012 |
| Starbang Limited | Manufacturing | 2001 |
| Starbill Limited | Professional & scientific | 2001 |
| Starfish Lettings Ltd | Real estate | 2025 |
| Stark Properties Limited | Real estate | 2017 |
| Starki Limited | Professional & scientific | 2019 |
| Starlight Event Productions Ltd | Arts & recreation | 2025 |
| Starlit Events Limited | Arts & recreation | 2017 |
| Starry Valleys Community Events CIC | Education | 2021 |
| Start Fresh Group Limited | Hospitality | 2022 |
| Start Smart Electrical Limited | Construction | 2021 |
| Start Smiling Again Limited | Health & social care | 2015 |
| Stasco Services Limited | Administrative & support | 1997 |
| Statemove Limited | Water & waste | 2015 |
| Static Caravan Repairs Ltd | Manufacturing | 2019 |
| Station Complex Limited | Other services | 2020 |
| Station Eighty SIX Limited | Hospitality | 2023 |
| Station Hill Garages Ltd | Manufacturing | 2013 |
| Statistical Analysis Solutions Ltd | Information & communication | 2014 |
| Staunch Tools Limited | Wholesale & retail | 2016 |
| Stavi Ltd | Other services | 2025 |
| Stay Gold Travel Ltd | Administrative & support | 2025 |
| Stay Gower Ltd | Real estate | 2021 |
| Stay Optimised Ltd | Health & social care | 2026 |
| Stay True Tattoo Studio Limited | Arts & recreation | 2017 |
| Stayfresh Limited | Wholesale & retail | 2024 |
| Stayfresh Studio Limited | Other services | 2019 |
| STC Group Limited | Financial services | 2025 |
| Steady Properties Ltd | Real estate | 2026 |
| Steak on the Kingsway Ltd | Hospitality | 2019 |
| Steel Feathers Limited | Construction | 2016 |
| Steel Interiors.Co Ltd | Construction | 2024 |
| Steel Supply (Property) Limited | Real estate | 1986 |
| Steel Supply Company(Western)Limited | Real estate | 1950 |
| Steele-Morgan Estates Limited | Real estate | 2023 |
| Steelenergy Consulting Limited | Professional & scientific | 2024 |
| Steeles Property Limited | Real estate | 2021 |
| Steelhead Limited | Professional & scientific | 2023 |
| Steldorn Limited | Administrative & support | 1996 |
| Stellar SPV Ltd | Real estate | 2019 |
| Stennah and Hope Limited | Manufacturing | 2013 |
| Stenor Environmental Services Ltd | Construction | 2003 |