| Sjthomas Limited | Real estate | 2025 |
| SN Property Management Ltd | Real estate | 2016 |
| Snowdrop Laundry & Dry-Cleaning Limited | Other services | 2016 |
| Solsen Renewables Ltd | Construction | 2023 |
| Sonder Commercial Ltd | Other services | 2020 |
| Sonder Property Developments Ltd | Real estate | 2023 |
| Soulfitness Ltd | Arts & recreation | 2018 |
| Sounds of the Underground Ltd | Information & communication | 2024 |
| South Wales Climbing Frames Limited | Construction | 2022 |
| Spider Studios Ltd | Information & communication | 2010 |
| Spud Village Ltd | Hospitality | 2026 |
| Square & Compass Inn Limited | Hospitality | 2002 |
| SRI Durga Devi Company Ltd | Health & social care | 2019 |
| Stallion Community Hub CIC | Arts & recreation | 2021 |
| Star Advanced Energy Limited | Construction | 2020 |
| Star Multifuels Limited | Other services | 2010 |
| Station Garage & MOT Centre Limited | Wholesale & retail | 2003 |
| Steada Limited | Construction | 2019 |
| Stitchandsew Crafts Ltd | Manufacturing | 2025 |
| Stobart Davies (2002) Limited | Information & communication | 2002 |
| Storehaus Limited | Information & communication | 2019 |
| Strawberry Software Ltd | Information & communication | 2020 |
| Studentproofreading.Co.Uk (Wales) Limited | Administrative & support | 2017 |
| Sunn Limited | Hospitality | 2022 |
| Superior Joinery Limited | Construction | 2000 |
| Superior Sheds Swansea Ltd | Manufacturing | 2019 |
| Supreme Motorsport Retail Ltd | Wholesale & retail | 2019 |
| Suraksha Ltd | Wholesale & retail | 2025 |
| Sureseal Windows Limited | Construction | 2016 |
| Sustainable Fuel Solutions Ltd | Administrative & support | 2019 |
| Swansea City Mission & Educational Trust | Health & social care | 2003 |
| Swansea Valley Carpentry Ltd | Construction | 2026 |
| Swelco Eighty Limited | Manufacturing | 1937 |
| Swpps Limited | Professional & scientific | 2021 |
| Synthetic Green Ltd | Construction | 2020 |
| T&C Hospitality Ltd | Hospitality | 2024 |
| T.Richard Jones (Betws)Limited | Construction | 1971 |
| Taff Scaffolding Ltd | Construction | 2019 |
| TAI Chapman Limited | Real estate | 2021 |
| TAI Dinefwr Limited | Construction | 2007 |
| TAI Grill Ltd | Hospitality | 2024 |
| Tairgwaith Community Club Ltd | Hospitality | 2021 |
| TAJ MB Ltd | Hospitality | 2019 |
| Talley Tea Rooms Ltd | Hospitality | 2018 |
| Tana Holdings Limited | Other services | 2024 |
| Tawny Consulting Ltd | Professional & scientific | 2021 |
| TDA Associates Limited | Other services | 2013 |
| Tdjrt Ltd | Manufacturing | 2021 |
| Tdjrt Vans Ltd | Manufacturing | 2022 |
| Tech Ascend Foundation Limited | Other services | 2025 |
| Techpoint Services Limited | Real estate | 2021 |
| Teilo Components Ltd | Manufacturing | 2007 |
| Teknosis Ltd | Information & communication | 2016 |
| Testpro Electrical Ltd | Construction | 2023 |
| TGD Solutions Limited | Professional & scientific | 2017 |
| THE Ammanford Congregational Church Conversion Ltd | Real estate | 2024 |
| THE Blindsman Limited | Manufacturing | 2002 |
| THE Boiler MAN (UK) Limited | Construction | 2010 |
| THE Carmarthenshire Rivers Trust | Agriculture & fishing | 2007 |
| THE Fencing Company Limited | Construction | 2025 |
| THE Ferry Pilots Ltd | Wholesale & retail | 2021 |
| THE Four Seasons (Pembrokeshire) Limited | Wholesale & retail | 2005 |
| THE Integrative Health Sciences Centre CIC | Education | 2025 |
| THE IVY Bush Inn Ltd | Hospitality | 2024 |
| THE Lighthouse Carmarthen Ltd | Wholesale & retail | 2022 |
| THE New Manford House Limited | Hospitality | 2025 |
| THE Original Tram Company Limited | Hospitality | 2021 |
| THE Raven Freehouse Ltd | Hospitality | 2026 |
| THE Retreat Canine Hydrotherapy & Wellness Ltd | Professional & scientific | 2018 |
| THE Seal Community C.I.C. | Other services | 2012 |
| THE Spinning Arrow Project Ltd | Arts & recreation | 2023 |
| THE Trade Post Ltd | Hospitality | 2023 |
| THE Travel Curator Ltd | Administrative & support | 2023 |
| THE Vape Room Group Ltd | Wholesale & retail | 2026 |
| Thermal Earth Limited | Construction | 2007 |
| Thompson Stem Engagement Cwmni Buddiant Cymunedol | Education | 2020 |
| Thorneycroft Boiler Maintenance Limited | Manufacturing | 2005 |
| Timber Tech Systems Ltd | Construction | 2025 |
| Timbercraft Construction Ltd | Construction | 2017 |
| TIR Y Dail Taxies Ltd | Transport & logistics | 2012 |
| Tirydail Motor Repairs Limited | Wholesale & retail | 2013 |
| TJ Aviation Ltd | Transport & logistics | 2023 |
| TJC Lifting Gear Limited | Manufacturing | 2012 |
| TL Air Solutions Ltd | Transport & logistics | 2024 |
| Tmorris Aviation Ltd | Manufacturing | 2016 |
| Tony Powell Farm Limited | Agriculture & fishing | 2026 |
| Tony Powell Transport Limited | Transport & logistics | 2002 |
| Total Property Renovations Ltd | Construction | 2020 |
| TRANS4 Ltd | Wholesale & retail | 2014 |
| Transwaste Limited | Water & waste | 1995 |
| Tregib Sports Facilities Ltd | Arts & recreation | 2016 |
| Triple C IT Limited | Information & communication | 2011 |
| Two Dragons Ammanford Ltd | Arts & recreation | 2025 |
| Two Eight Zero Five Consultancy Ltd | Professional & scientific | 2021 |
| TY Coch Construction Ltd | Construction | 2019 |
| TY Coch Properties Ltd | Real estate | 2019 |
| TY Tanerdy Ltd | Hospitality | 2025 |
| Tycroes Driving Range Limited | Arts & recreation | 2006 |
| Tycroes RFC Limited | Arts & recreation | 2010 |
| Tywi Specialists Limited | Construction | 2001 |