| SEV Design Ltd | Professional & scientific | 2024 |
| Seven Testing Services Limited | Professional & scientific | 2010 |
| Seventeen Oaks Limited | Real estate | 2006 |
| Severn Environmental Engineering Limited | Manufacturing | 1993 |
| Severn Seed Finance Limited | Professional & scientific | 2016 |
| SH Aviation Contractors Limited | Other services | 2025 |
| SH Holdings Limited | Professional & scientific | 2025 |
| Shark Bite Burgers Limited | Hospitality | 2021 |
| Sharkbite Burgers Delivery Limited | Hospitality | 2023 |
| Sharkbite Burgers Platform Limited | Hospitality | 2026 |
| Sharkbite Eats Limited | Hospitality | 2025 |
| Sharkbites Eats Limited | Hospitality | 2025 |
| Sharks Deli Limited | Hospitality | 2025 |
| Sherborne Walk Management Limited | Households | 2003 |
| Shuffleer Limited | Information & communication | 2022 |
| Sifility Property Management Ltd | Real estate | 2018 |
| Silcox Stores Limited | Administrative & support | 2012 |
| Silent Disco Party (UK) Limited | Administrative & support | 2021 |
| Silhouette Business Support Ltd | Professional & scientific | 2026 |
| Silverback Systems Services Limited | Administrative & support | 2015 |
| Silverline Property Empire Ltd | Real estate | 2026 |
| Silverline Property Investment Group Ltd | Real estate | 2024 |
| Silverline Relocations Ltd | Hospitality | 2023 |
| Simple AI Solutions Ltd | Other services | 2023 |
| Simple Shopping Solutions Ltd | Wholesale & retail | 2023 |
| Simpson Motorsport Ltd | Wholesale & retail | 2003 |
| Sirch Solutions Limited | Administrative & support | 2016 |
| Sirhowy Investments Limited | Real estate | 1988 |
| Site Guardian Group Ltd | Administrative & support | 2021 |
| SJT Consulting Ltd | Professional & scientific | 2023 |
| Sjtk Golf Ltd | Arts & recreation | 2020 |
| SK Aerospace Ltd | Manufacturing | 2015 |
| Skin Sensation Piercing Ltd | Other services | 2025 |
| Skin Sensation Tattoo Ltd | Other services | 2025 |
| Skinscape Aesthetics UK Ltd | Other services | 2023 |
| Sky City UK Limited | Real estate | 2017 |
| Skyark Taxis Ltd | Transport & logistics | 2026 |
| Skyla Scaffolding Limited | Construction | 2017 |
| Slade Contractors Ltd | Construction | 2021 |
| SMA Travels Ltd | Transport & logistics | 2023 |
| Smart AI Systems Ltd | Professional & scientific | 2025 |
| Smart Darts Cwmbran Limited | Wholesale & retail | 2016 |
| Smart Energy Business Limited | Construction | 2023 |
| Smart Energy Group Ltd | Construction | 2015 |
| Smart Energy Holdings Limited | Financial services | 2023 |
| Smart Fuels Limited | Extraterritorial | 2004 |
| Smart Sanitising Systems Limited | Administrative & support | 2018 |
| Smart Stone Solutions Ltd | Wholesale & retail | 2020 |
| Smartbuy Garages Limited | Wholesale & retail | 2018 |
| Smiths Development Holdings Ltd | Real estate | 2025 |
| SML Trade Services Limited | Construction | 2026 |
| Sneak Peek Ultrasound Ltd | Wholesale & retail | 2025 |
| Snug Pizzeria Ltd | Hospitality | 2025 |
| Social Safeguarding Limited | Professional & scientific | 2025 |
| Solar Buddies Limited | Wholesale & retail | 2014 |
| Solar Medical & Chemical Limited | Manufacturing | 2017 |
| Sonas Developments Limited | Manufacturing | 2006 |
| Sonas Holdings Hereford Limited | Construction | 2015 |
| Sonnenalp Ventures Limited | Real estate | 2025 |
| Soundtrack Productions Limited | Information & communication | 2023 |
| Source 1 Utilities Limited | Construction | 2022 |
| South Auto Electrics Ltd | Manufacturing | 2018 |
| South Power Group Ltd | Construction | 2026 |
| South Wales Auctions Limited | Wholesale & retail | 2025 |
| South Wales Concrete Pumping Ltd | Construction | 2012 |
| South Wales Dog Training Ltd | Other services | 2023 |
| South Wales Screeding Services Ltd | Construction | 2013 |
| South Wales Switchgear Limited | Extraterritorial | 2015 |
| South Wales Transformers Limited | Manufacturing | 2015 |
| South Wales Vending Limited | Wholesale & retail | 2025 |
| Southard Group Limited | Administrative & support | 2023 |
| Southwood Investments (Cwmbran) Ltd | Real estate | 2016 |
| Spanner King Ltd | Wholesale & retail | 2024 |
| Sparkleguru Limited | Extraterritorial | 2021 |
| Sphere 86 Ltd | Real estate | 2020 |
| Spikey Frogs Gamestore Ltd | Wholesale & retail | 2023 |
| Sport Memories Limited | Wholesale & retail | 2003 |
| Sport Safeguarding Limited | Professional & scientific | 2018 |
| Spotless Window Cleaning Supplies Ltd | Wholesale & retail | 2022 |
| Springvale Car Sales Limited | Wholesale & retail | 2014 |
| Springvale Property Investments Ltd | Households | 2019 |
| Squire-N Electrical (Wales) Limited | Construction | 2026 |
| Sree Trading Ltd | Wholesale & retail | 2014 |
| SSD Hospitality Ltd | Hospitality | 2025 |
| Ssjs Property Limited | Real estate | 2020 |
| SSN Asset Hire Limited | Administrative & support | 2016 |
| ST Paving Limited | Construction | 2020 |
| Stacktiger Ltd | Information & communication | 2020 |
| Stadium House Apartments Ltd | Real estate | 2025 |
| Stafford Computer Technology Limited | Information & communication | 1992 |
| Stage Key Ltd. | Arts & recreation | 2012 |
| Star Phone Repairs Limited | Other services | 2025 |
| Starlet Farming Limited | Manufacturing | 2019 |
| Starlight Management Services Limited | Real estate | 2012 |
| Station Properties (Cwmbran) Ltd. | Hospitality | 2015 |
| Stax Property Ltd | Real estate | 2024 |
| Stay Onside Ltd | Public administration | 2025 |
| Steeple View 1966 Limited | Extraterritorial | 2014 |
| Steltec Holdings Limited | Manufacturing | 2019 |
| Steve Evans Logistics Ltd | Wholesale & retail | 2016 |