| Saunder Developments Ltd | Construction | 2019 |
| Saunders & Sons Bricklaying Limited | Construction | 2019 |
| Saundersway Properties Limited | Hospitality | 1971 |
| Save Gowerton From Gridlock Ltd | Professional & scientific | 2026 |
| Save OUR Seized Dogs Ltd | Other services | 2019 |
| Savelow Limited | Wholesale & retail | 1997 |
| Savitar Drinks Limited | Manufacturing | 2023 |
| Savslogistics Ltd | Transport & logistics | 2023 |
| SAW NK Limited | Health & social care | 2017 |
| Sawik Ltd | Transport & logistics | 2017 |
| Sawna Bach Ltd | Wholesale & retail | 2023 |
| Sayaanir Ltd | Construction | 2025 |
| Sayam Poultry Ltd | Wholesale & retail | 2021 |
| Sazs Travel Ltd | Transport & logistics | 2021 |
| SB Law Limited | Administrative & support | 2011 |
| SB Property 84 Ltd | Real estate | 2025 |
| SB Property Acquisition Limited | Real estate | 2024 |
| SBG Hills Ltd | Professional & scientific | 2025 |
| SBJ Developments Limited | Professional & scientific | 2014 |
| Sbmr Properties Ltd | Real estate | 2022 |
| SBR International Ltd | Wholesale & retail | 2023 |
| SBW Ltd | Construction | 2024 |
| SC School of Motoring Ltd | Education | 2022 |
| SC Storage Ltd Limited | Transport & logistics | 2023 |
| Scaffolding Stronghold Ltd | Construction | 2018 |
| Scarecrow Consultants Limited | Information & communication | 2014 |
| Scarlet Design Limited | Professional & scientific | 2022 |
| Scarlet Ribbon Merino Ltd | Manufacturing | 2014 |
| Scene & Word Limited | Arts & recreation | 2006 |
| Scenerotor Limited | Professional & scientific | 2002 |
| Scentra Ltd | Wholesale & retail | 2025 |
| Scents by the Sea Limited | Wholesale & retail | 2024 |
| Scents of Solitude Ltd | Wholesale & retail | 2021 |
| Schleswick & SON Limited | Construction | 2022 |
| School of Play and Creative Therapies Ltd | Education | 2023 |
| Schoolhouse Daycare Limited | Education | 2002 |
| Scibionano Ltd | Professional & scientific | 2022 |
| Science Matters Ltd | Education | 2022 |
| Scientific Cloud Limited | Professional & scientific | 2020 |
| Scientific Cloud Properties Limited | Real estate | 2023 |
| Scimh Ltd | Financial services | 2020 |
| Scomax Ltd | Real estate | 2024 |
| Scorpion Joystick Ltd | Administrative & support | 2023 |
| Scorpion M&E Services Ltd | Construction | 2021 |
| Scott Burrows Company Limited | Construction | 2016 |
| Scott Burrows Developments Limited | Real estate | 2017 |
| Scott Griffiths Ltd | Information & communication | 2019 |
| Scott Jenkins Interior Solutions Ltd | Construction | 2025 |
| Scott Jones Building Limited | Construction | 2025 |
| Scotts Exteriors Limited | Wholesale & retail | 2023 |
| Scout Technologies Limited | Information & communication | 2023 |
| Scout-Swansea Ltd | Financial services | 2020 |
| SCP Assets Ltd | Real estate | 2015 |
| Scrapline Metals Ltd | Wholesale & retail | 2025 |
| Scriptor Cube Ltd | Education | 2017 |
| Scrubbers (SW) Ltd | Administrative & support | 2018 |
| Scrubchit Company Limited | Health & social care | 2024 |
| Scruffy Films Ltd | Information & communication | 2017 |
| Scrumr Limited | Arts & recreation | 2026 |
| Sctradingcards Limited | Extraterritorial | 2025 |
| Scuffed UP Limited | Wholesale & retail | 2017 |
| Scully Property Group Ltd | Construction | 2021 |
| Sculpt by Wisdom Ltd | Professional & scientific | 2025 |
| Sculpture by the Sea UK Ltd | Arts & recreation | 2012 |
| Scurlage Apothecary Limited | Health & social care | 2025 |
| Scwba Limited | Extraterritorial | 2023 |
| Scy-Tron Ltd | Information & communication | 2013 |
| Scylding Group Limited | Administrative & support | 2015 |
| Scythia Brands Ltd | Wholesale & retail | 2020 |
| SD Tyre Services Limited | Wholesale & retail | 2025 |
| SDF Social Limited | Other services | 2026 |
| SDL Inspection Limited | Professional & scientific | 2015 |
| SDS Precision Engineering Limited | Manufacturing | 2007 |
| SE & AL Properties Limited | Households | 2025 |
| Sea Property Services Ltd | Real estate | 2025 |
| Sea View (Mumbles) Management Limited | Households | 1980 |
| Sea, Land & Air Ltd | Wholesale & retail | 2025 |
| Sea-Lift Diving Limited | Manufacturing | 1991 |
| Seabreeze Homes & Properties Ltd | Real estate | 2019 |
| Seaflex Ltd | Professional & scientific | 2026 |
| Seager Property Limited | Real estate | 2012 |
| Seahop Limited | Real estate | 2011 |
| Sealand Properties Ltd | Administrative & support | 2003 |
| Sealpro Limited | Construction | 2020 |
| Sean Hirst Transformations Ltd | Construction | 2015 |
| Sean Ltd | Construction | 2010 |
| Sean Moran Accounting Services Limited | Professional & scientific | 2018 |
| Searchlight Limited | Real estate | 2017 |
| Searchlight Mortgages Ltd | Financial services | 2020 |
| Sears Business Park Limited | Real estate | 2026 |
| Sears Landlords Ltd | Real estate | 2017 |
| Sears Property Holdings Ltd | Real estate | 2018 |
| Seasans Carriage Company Limited | Wholesale & retail | 2023 |
| Seaward Fitness Ltd | Arts & recreation | 2025 |
| Seaward Management Company Limited | Real estate | 2018 |
| Seba Couriers Ltd | Transport & logistics | 2022 |
| Second Life Products Wales Limited | Manufacturing | 2010 |
| Second Life Properties Limited | Real estate | 2025 |
| Secpro Limited | Administrative & support | 2011 |
| Secret Sauna Escape Ltd | Health & social care | 2024 |