| Stenor Limited | Administrative & support | 2010 |
| Step by Step Care and Support Ltd | Health & social care | 2024 |
| Stephar (U.K.) Limited | Wholesale & retail | 1983 |
| Stephen Hughes Limited | Wholesale & retail | 1995 |
| Stephen Parry Limited | Health & social care | 2006 |
| Stephen Pritchard Energy Assessor Ltd | Construction | 2024 |
| Stephen Sarasin Limited | Health & social care | 2016 |
| Stephenson Alexander Astleys Ltd | Real estate | 2024 |
| Stephoma Luxury Hair Ltd | Wholesale & retail | 2026 |
| Stepping in 4 YOU C.I.C. | Health & social care | 2022 |
| Sterimelt Technologies Ltd | Manufacturing | 2012 |
| Sterling Business Services (Wales) Ltd | Professional & scientific | 2003 |
| Sterling Mortgages and Protection Ltd | Financial services | 2010 |
| Sterling Peak Holdings Ltd | Other services | 2019 |
| Sterling Rees Limited | Professional & scientific | 2006 |
| Sterling Way Online Ltd | Wholesale & retail | 2025 |
| Sterling Welsh Limited | Financial services | 2015 |
| Sterling Wings Ltd | Transport & logistics | 2021 |
| Steve Combe Governance Ltd | Public administration | 2019 |
| Steve Morgan Wire ROD Limited | Professional & scientific | 2019 |
| Steve Pope & SON Transport Ltd | Transport & logistics | 2012 |
| Steven Davies Plumbing & Heating Ltd | Construction | 2018 |
| Steven R Elliot & Co Limited | Professional & scientific | 2008 |
| Steven Richard Homer Ltd | Extraterritorial | 2024 |
| Steven T Holdings Ltd | Administrative & support | 2019 |
| Stevic Ltd | Administrative & support | 2025 |
| Stewart Bros Ltd | Construction | 2023 |
| Steyn Trading Ltd | Wholesale & retail | 2020 |
| Stiddard Limited | Financial services | 2008 |
| Stiddard Wealth UK Limited | Financial services | 2012 |
| Stiens Haulage Limited | Transport & logistics | 1999 |
| Stiens Waste Recycling Limited | Water & waste | 2017 |
| Stillrow Limited | Wholesale & retail | 2018 |
| Stiwdio 'NI' Ltd | Arts & recreation | 2026 |
| Stone & Stove Ltd | Professional & scientific | 2015 |
| Stone and Brick Supplies Limited | Administrative & support | 2018 |
| Stone Hospitality Limited | Hospitality | 2013 |
| Stoned Kids International LLP | | 2017 |
| Stonehaven Property Ltd | Real estate | 2025 |
| Stonelake Group Ltd | Construction | 2024 |
| Stones & Co Insolvency Practitioners Limited | Financial services | 2019 |
| Stoney Wall Holdings Limited | Real estate | 2022 |
| Stop & Shop Express Ltd | Wholesale & retail | 2022 |
| Storage Brother Limited | Administrative & support | 2025 |
| Storage Co. (Wales) Ltd | Real estate | 2024 |
| Storage Lady Limited | Administrative & support | 2025 |
| Store ALL Wales Ltd | Transport & logistics | 2020 |
| Store Anything Limited | Administrative & support | 2023 |
| STORE24.TODAY Limited | Other services | 2024 |
| Storii Ltd | Information & communication | 2025 |
| Storm in a Teacup Coffeehouse Limited | Hospitality | 2018 |
| Stormrider Limited | Professional & scientific | 2015 |
| Stormshield Roofing Limited | Construction | 2012 |
| Storr Rock Limited | Construction | 2002 |
| Storr Rock Management Company Limited | Households | 2019 |
| Stouthall Towers Limited | Hospitality | 2026 |
| Strasdin Estates Limited | Real estate | 2024 |
| Strasdin Joinery Limited | Manufacturing | 2007 |
| Strata Properties Limited | Real estate | 2020 |
| Stravan Ltd | Administrative & support | 2025 |
| Strawberry Close Management Company Ltd | Households | 2003 |
| Streamline Development South Wales Limited | Construction | 2025 |
| Streamline Leisure Holdings Ltd | Financial services | 2019 |
| Streamline Leisure Limited | Hospitality | 2007 |
| Street Traffic Limited | Professional & scientific | 2026 |
| Streetloom Tees Ltd | Manufacturing | 2026 |
| Streetmaster (South Wales) Limited | Manufacturing | 2007 |
| Strength LAB Ltd | Arts & recreation | 2018 |
| Strider Group Ltd | Administrative & support | 2025 |
| Strinati Limited | Construction | 2018 |
| Strive Active Limited | Arts & recreation | 2024 |
| Strive Creations Ltd | Manufacturing | 2015 |
| Strive Online Coaching Ltd | Education | 2021 |
| Stronach & Stronach Limited | Financial services | 2003 |
| Structural Test Services Limited | Professional & scientific | 2024 |
| Structures & Civils Limited | Construction | 2012 |
| Stryke Events & Security Limited | Administrative & support | 2022 |
| STS 22 Star Transport Solutions Ltd | Transport & logistics | 2022 |
| Stuart Collins & Co Limited | Financial services | 2021 |
| Stuart Davies Consulting Ltd | Professional & scientific | 2019 |
| Stuarts Artisan Bakery CYF | Manufacturing | 2023 |
| Stuarts Skip Hire Ltd | Water & waste | 2014 |
| Student Select Swansea Ltd | Real estate | 2021 |
| Studentdigz Ltd | Real estate | 2021 |
| Studio 808 Ltd | Information & communication | 2021 |
| Studio BCC Ltd | Professional & scientific | 2025 |
| Studio Benia Ltd | Professional & scientific | 2024 |
| Studio by EVA Limited | Wholesale & retail | 2022 |
| Studio-Drinks Limited | Wholesale & retail | 2024 |
| Studts Events Holdings Limited | Financial services | 2025 |
| Studts Events Limited | Arts & recreation | 2016 |
| Sturgess Mortgage Solutions Ltd | Financial services | 2022 |
| Sturgess Property Group Ltd | Real estate | 2024 |
| Style Master Limited | Other services | 2015 |
| Style UN Limited | Extraterritorial | 2023 |
| Stylechase Limited | Real estate | 2002 |
| Styledge Ltd | Manufacturing | 2020 |
| Stylegrange Limited | Wholesale & retail | 2002 |
| SU Pathway College Limited | Professional & scientific | 2017 |
| Suaeda Marine Ltd | Professional & scientific | 2021 |