| SET the Scene Design Limited | Professional & scientific | 2005 |
| Sexton Davies Properties Limited | Real estate | 2003 |
| SH Hair Beauty Ltd | Other services | 2025 |
| Shadow Holdings Limited | Real estate | 2001 |
| Shadow Rigging Limited | Construction | 2016 |
| Shannon Energy UK Limited | Professional & scientific | 2023 |
| Shaun Baker Estates Ltd | Real estate | 2025 |
| Shawcast Limited | Extraterritorial | 2025 |
| Shaws Scaffolding Specialists Ltd | Construction | 2021 |
| Shearan Safety Ltd | Public administration | 2023 |
| Sheds Centre Wales Limited | Wholesale & retail | 2010 |
| Shefinance Ltd | Education | 2024 |
| Shengyuan Limited | Hospitality | 2026 |
| Shepherds the Vets Limited | Professional & scientific | 2006 |
| Shepherds TY ARC Properties Ltd | Professional & scientific | 2016 |
| Shermark Enterprises Limited | Hospitality | 2007 |
| Shermark Holdings Limited | Hospitality | 2015 |
| Shield Serv. Facilities Management Ltd | Administrative & support | 2022 |
| Shillibiers Limited | Water & waste | 2016 |
| Shine Diamond Cleaning Ltd | Administrative & support | 2025 |
| Shireash Limited | Extraterritorial | 2026 |
| Shiredon Limited | Wholesale & retail | 2024 |
| Shirelea Limited | Extraterritorial | 2025 |
| Shireray Limited | Other services | 2024 |
| Shirerow LLP | | 2023 |
| Shirker Transport Ltd | Transport & logistics | 2025 |
| SHL 1 Limited | Construction | 2011 |
| SHL Hire Ltd | Administrative & support | 2011 |
| Shogun Games Limited | Information & communication | 2024 |
| Siam Construction Services Ltd | Construction | 2016 |
| Sidehelm Limited | Extraterritorial | 2025 |
| Sienna Signs Ltd | Manufacturing | 2025 |
| Sigma Marine Technologies Limited | Information & communication | 2014 |
| Silent Night Films Ltd | Information & communication | 2012 |
| Silicon Road Ltd | Wholesale & retail | 2025 |
| Siloclean Services Ltd | Administrative & support | 2025 |
| Silver Lining Real Estate Ltd | Real estate | 2026 |
| Silver Lining Rentals Limited | Real estate | 2023 |
| Silvercrest Care Homes Limited | Health & social care | 2014 |
| Silvercrown Care Homes (Pontypridd) Limited | Health & social care | 1997 |
| Silvercrown Care Homes (Swansea) Limited | Health & social care | 2005 |
| Silvercrown Care Homes Ltd | Health & social care | 2015 |
| Simeon Thomas Heating and Plumbing Engineers Limited | Construction | 2024 |
| Simon Aberstone Ltd | Construction | 2015 |
| Simon Blake Forklift Tyres Limited | Manufacturing | 2016 |
| Simon Lake Consultancy Limited | Professional & scientific | 2024 |
| Simple Gadgets Limited | Wholesale & retail | 2011 |
| Simply OUT of School Ltd | Education | 2006 |
| Simpology UK Limited | Information & communication | 2003 |
| Sinclair Finance and Leasing Company Limited | Wholesale & retail | 1986 |
| Sinclair Garages (Bridgend) Limited | Wholesale & retail | 1981 |
| Sinclair Garages (Cardiff) Limited | Wholesale & retail | 2008 |
| Sinclair Garages (Newport) Ltd. | Wholesale & retail | 1990 |
| Sinclair Garages (Port Talbot) Limited | Wholesale & retail | 1974 |
| Sinclair Garages (Swansea) Limited | Wholesale & retail | 2007 |
| Sinclair Garages Limited | Wholesale & retail | 1977 |
| Sinclair Motor Holdings Limited | Wholesale & retail | 2002 |
| Sinclair OPS Ltd | Financial services | 2021 |
| Single Steps Learning Ltd | Education | 2015 |
| Singleton Davies Group Ltd | Wholesale & retail | 2023 |
| Singletons Executive Cars Limited | Transport & logistics | 2017 |
| Sirensys Limited | Information & communication | 2024 |
| SIS Fire and Security Limited | Administrative & support | 2025 |
| Sixx CNC Limited | Manufacturing | 2019 |
| SJ8 Properties Limited | Real estate | 2023 |
| SJC Rail Solutions Ltd | Construction | 2014 |
| SJH Consulting (Insulation) Limited | Professional & scientific | 2017 |
| SJM Roofing Solutions Ltd | Construction | 2026 |
| SJN Property Limited | Real estate | 2019 |
| Sjp-Med Ltd | Health & social care | 2014 |
| SJW Aviation Limited | Manufacturing | 2025 |
| SK Daily Basket Limited | Wholesale & retail | 2026 |
| SK Worldwide Ltd | Transport & logistics | 2025 |
| Skerryback Farm Cottages LLP | | 2005 |
| Skinner Family Entertainment Ltd | Arts & recreation | 2024 |
| Sklep U Pauli Ltd. | Wholesale & retail | 2014 |
| Sky Couriers SW Ltd | Transport & logistics | 2025 |
| Skyland Hotels Limited | Hospitality | 2001 |
| Skylark Works Ltd | Professional & scientific | 2020 |
| Slick Vixen Beauty Lounge Ltd | Other services | 2023 |
| Slimtone Ltd | Extraterritorial | 2012 |
| SLJ Consult Limited | Transport & logistics | 2026 |
| SLN Home Improvements Ltd | Construction | 2025 |
| SLS Ventures Ltd | Information & communication | 2024 |
| Sludge Budgers Ltd | Construction | 2026 |
| Small Village Big Business Ltd | Manufacturing | 2022 |
| Smart Education Tuition Wales Limited | Education | 2019 |
| Smart Home Emporium Limited | Wholesale & retail | 2023 |
| Smart HR (Bridgend) Limited | Administrative & support | 2026 |
| Smart Lettings (Bridgend) Limited | Real estate | 2021 |
| Smart Property Maintenance (Bridgend) Limited | Construction | 2021 |
| Smartlend Ltd | Financial services | 2023 |
| Smartpac Limited | Administrative & support | 2012 |
| SMD Lina Limited | Health & social care | 2016 |
| Smebb Ltd | Real estate | 2022 |
| Smecluster Network Limited | Other services | 2021 |
| SMF Investments Limited | Extraterritorial | 2022 |
| SMG (Kent) Limited | Manufacturing | 2003 |
| Smith Advisory Limited | Professional & scientific | 2011 |
| Snack VPN App Limited | Wholesale & retail | 2025 |