| Star Foods (Bettws) Ltd | Hospitality | 2025 |
| Star International Food Ltd | Wholesale & retail | 2022 |
| Star Takeway Ltd | Hospitality | 2018 |
| Starc Limited | Information & communication | 2009 |
| Starlight Crafts Ltd | Wholesale & retail | 2006 |
| Starlux Homes Limited | Real estate | 2025 |
| Starmaster Limited | Education | 2026 |
| Startsafe Limited | Administrative & support | 1986 |
| Startspin Limited | Extraterritorial | 2005 |
| Stay Care Operations Ltd | Water & waste | 2025 |
| Staycatering Events Ltd | Hospitality | 2021 |
| STC Financial Ltd | Financial services | 2015 |
| Stealth Valeting Ltd | Administrative & support | 2022 |
| Steddy Employee Ownership Trustee Limited | Professional & scientific | 2023 |
| Steddy Limited | Wholesale & retail | 2004 |
| Steels Management Limited | Professional & scientific | 1982 |
| Stefano Foods Ltd | Hospitality | 2026 |
| Stefmar Haulage Ltd | Transport & logistics | 2023 |
| Step Podiatry Limited | Health & social care | 2017 |
| Stephanchristopher Ltd | Agriculture & fishing | 2024 |
| Stereotype Tattoo Studio Ltd | Arts & recreation | 2025 |
| Steve David & Sons Ltd | Construction | 2012 |
| Steve Richmond Limited | Wholesale & retail | 2008 |
| STI Spedition Ltd | Transport & logistics | 2020 |
| Sticky Fingers Sweet Treats Limited | Hospitality | 2025 |
| Stillpoint Group Ltd | Wholesale & retail | 2025 |
| Stone and Glass Group Limited | Wholesale & retail | 2007 |
| Stonefox Limited | Administrative & support | 2025 |
| Stonehouse Coffee Beans Ltd | Wholesale & retail | 2024 |
| Storm Security Ltd | Administrative & support | 2024 |
| Stormy Down Property Wales Limited | Real estate | 2009 |
| Stormy Down Recycling Ltd | Extraterritorial | 2014 |
| Stormy Farm Limited | Construction | 2018 |
| Storm’S Clearances Ltd | Transport & logistics | 2025 |
| Strategic Building Solutions Ltd | Construction | 2025 |
| Stratford Collins Associates Limited | Construction | 2012 |
| Stratford Collins Build & Design Limited | Construction | 2014 |
| Stratford Collins Consultants Limited | Financial services | 2006 |
| Stratton Mortgages Ltd | Financial services | 2021 |
| Stratton Wills and Estate Planning Ltd | Financial services | 2025 |
| Street Lighting Services Limited | Construction | 1998 |
| Stride Financial Management Ltd | Financial services | 2021 |
| Structura Holdings Limited | Financial services | 2025 |
| Stuart Floyd-Ellis Limited | Construction | 2024 |
| Stuart Health Limited | Administrative & support | 2002 |
| Stump Monkey Ltd | Construction | 2022 |
| Styleforce Limited | Extraterritorial | 2006 |
| SUE Davies Consultancy Limited | Professional & scientific | 2016 |
| SUE John Therapies Ltd | Health & social care | 2024 |
| SUE Raikes Limited | Health & social care | 2014 |
| Summer Agency Limited | Real estate | 1993 |
| SUMMITK2 Limited | Arts & recreation | 2017 |
| SUMMITK2CAFE Limited | Hospitality | 2025 |
| Sunlight Blinds Limited | Professional & scientific | 2004 |
| Sunny Collaborative Support Limited | Health & social care | 2024 |
| Sunny’S Giveaways Ltd | Arts & recreation | 2026 |
| Sunrise Interiors Limited | Wholesale & retail | 1998 |
| Sunrise Leaders LLP | | 2021 |
| Support Around the World Ltd | Information & communication | 2024 |
| Support Pen-Y-Bont Ltd | Wholesale & retail | 2006 |
| SUPPORT4OMEGA Ltd | Information & communication | 2004 |
| Supreme Roofers Limited | Construction | 2024 |
| Supreme Screen Prints Ltd | Manufacturing | 2017 |
| Surefit Roofing Limited | Construction | 2025 |
| Surge Electrical Engineering Ltd | Energy | 2018 |
| Surge Renewable Energy Ltd | Construction | 2024 |
| Sustainable Eco Developments (Wales) Limited | Construction | 2021 |
| SVB Creative Consulting Limited | Professional & scientific | 2022 |
| Sven Sports Ltd | Manufacturing | 2025 |
| Sven's Deli & Desserts Ltd | Hospitality | 2025 |
| SW Gaming HUT Limited | Other services | 2023 |
| SW Home & Garden Limited | Wholesale & retail | 2012 |
| SW Tape & Jointing Limited | Construction | 2018 |
| SW Van Conversions & Sales Limited | Manufacturing | 2017 |
| Swanac Publichouse Limited | Hospitality | 2025 |
| Swansea Laser Clinic Ltd | Health & social care | 2015 |
| Swansea TPS Limited | Wholesale & retail | 2007 |
| SWE Property Ltd | Construction | 2026 |
| Swec Ltd | Agriculture & fishing | 2023 |
| Swift Haulage Solutions Limited | Transport & logistics | 2016 |
| Swiftening Limited | Information & communication | 2012 |
| Swimkidz Berkshire LLP | | 2013 |
| Swimkidz Franchise Limited | Administrative & support | 2011 |
| Swiss Vans Limited | Administrative & support | 2010 |
| Switch Contractor Services Ltd | Construction | 2018 |
| SWN YR Afon Management Limited | Extraterritorial | 2011 |
| SYD Rentals Limited | Construction | 2025 |
| Sygnium Ltd | Professional & scientific | 2018 |
| Sylfaen Developments Limited | Extraterritorial | 2025 |
| Sylfaen Homes Limited | Construction | 2025 |
| Symco Digital Ltd | Information & communication | 2019 |
| Synapse-Id Limited | Information & communication | 2025 |
| Synergy Autos Ltd | Wholesale & retail | 2019 |
| Synergy Construction Management Limited | Construction | 2022 |
| Sysnet Limited | Information & communication | 1982 |
| Sysqo Limited | Professional & scientific | 2022 |
| T & G Property Maintenance Ltd | Manufacturing | 2025 |
| T & NL Holdings Ltd | Financial services | 2024 |
| T & NL Property Ltd | Real estate | 2021 |
| T & T General Stores Ltd | Wholesale & retail | 2022 |