| Sasira Ltd | Information & communication | 2019 |
| Sasselina Consulting Ltd | Professional & scientific | 2019 |
| Savo's Pizza Ltd | Hospitality | 2018 |
| Scandal BG Ltd | Hospitality | 2019 |
| Scent-Sation WAX Limited | Wholesale & retail | 2017 |
| SCH Engineering Services Ltd | Construction | 2023 |
| Scorpion Site Services Limited | Administrative & support | 2023 |
| Scourfield GAS Services Ltd | Construction | 2022 |
| Sea Grey Design Ltd | Construction | 2016 |
| Sean's Driving Service Ltd | Transport & logistics | 2020 |
| Select Signs Limited | Manufacturing | 1999 |
| Senseiv Ltd | Professional & scientific | 2022 |
| Seren Support Services Ltd | Health & social care | 2011 |
| SGS Investment Holdings Ltd | Real estate | 2022 |
| Shah & Son's Ltd | Real estate | 2026 |
| Sheds Ahead Limited | Manufacturing | 2010 |
| Shepwell Commercial Properties Ltd | Real estate | 2024 |
| Shepwell Group Ltd | Administrative & support | 2021 |
| Shepwell Properties Ltd | Real estate | 2021 |
| Shexa Vape Ltd | Wholesale & retail | 2025 |
| Shining Star Entertainment Ltd | Professional & scientific | 2025 |
| Shorefire Limited | Other services | 2024 |
| Shoreline Investments Limited | Real estate | 2019 |
| Shoreline Rental Properties LLP | | 2020 |
| Shri Kalpaga Hindu Cultural Association | Health & social care | 2013 |
| SHV Services Limited | Professional & scientific | 2016 |
| Sierra Papa Victor Limited | Real estate | 2026 |
| Signal Enhancement Diagnostics Limited | Administrative & support | 2024 |
| Signature Assessments Ltd | Professional & scientific | 2026 |
| Signature Beauty Lounge & Training Ltd | Education | 2024 |
| Signature Car Hub Ltd | Wholesale & retail | 2025 |
| Signature Living Solutions Ltd | Manufacturing | 2025 |
| Silver Birch Property Group Ltd | Real estate | 2025 |
| Sindicut Barbershop Ltd | Other services | 2025 |
| Site Desk Ltd | Administrative & support | 2026 |
| Site Heat Treatment Services (GB) Limited | Extraterritorial | 2012 |
| Site Heat Treatment Services (UK) Limited | Extraterritorial | 1991 |
| Site Heat Treatment Services Limited | Construction | 1981 |
| Site Smart Timber Frame Solutions Ltd | Construction | 2023 |
| Sitepilot Ltd | Professional & scientific | 2026 |
| SJB Creative Designs Ltd | Wholesale & retail | 2020 |
| SJB Innovates Limited | Professional & scientific | 2026 |
| Sjdpilatesteachertrainingacademy Ltd | Education | 2025 |
| SJE Electrical Services Ltd | Real estate | 2024 |
| SK FOODS21 Limited | Hospitality | 2025 |
| SK Kenfig Hill Ltd | Hospitality | 2025 |
| SK Lane Properties Ltd | Real estate | 2024 |
| Skineerino Ltd | Administrative & support | 2020 |
| SL Property South Wales Ltd | Construction | 2025 |
| SLC Property Holding UK Ltd | Financial services | 2023 |
| SLC Training UK Ltd | Education | 2023 |
| Slkg Limited | Administrative & support | 2015 |
| SM & SON Holding Limited | Real estate | 2025 |
| Smarrt Consultancy and Training Ltd | Professional & scientific | 2026 |
| Smart Scaffolding Solutions Limited | Construction | 2019 |
| SMC Marine Ltd | Construction | 2022 |
| Smith Electrical (Brombil) Ltd | Construction | 2021 |
| Snowsea Ltd | Hospitality | 2020 |
| Sodem Action Limited | Other services | 2022 |
| Sofanet Ltd | Wholesale & retail | 2024 |
| Soft Washing Wales Ltd | Administrative & support | 2023 |
| Solstice Therapies Ltd | Health & social care | 2023 |
| Solutions to Structures Ltd | Construction | 2009 |
| Sophia Real Estates Ltd | Real estate | 2023 |
| Sophia Store Ltd | Wholesale & retail | 2017 |
| Soulandpepper Food Limited | Hospitality | 2024 |
| South Coast Plantation Shutters Ltd | Wholesale & retail | 2021 |
| South Trails Dog Walking Ltd | Professional & scientific | 2022 |
| South Wales Civils Limited | Construction | 2025 |
| South Wales Construction Ltd. | Manufacturing | 2018 |
| South Wales Electrical Training Limited | Administrative & support | 2008 |
| South Wales Environmental Limited | Administrative & support | 2004 |
| South Wales Industrial Equipment Limited | Manufacturing | 2001 |
| South Wales Supplies Limited | Wholesale & retail | 1996 |
| South Wales Towbars Ltd | Wholesale & retail | 2025 |
| Southall Social Work Assessment Ltd | Health & social care | 2023 |
| Sparky-Solutions Ltd | Construction | 2014 |
| Spice Cube (Ammanford) Ltd | Hospitality | 2011 |
| Spice Cube 21 Ltd | Hospitality | 2021 |
| Springfield Advisory Ltd | Health & social care | 2023 |
| Spud FAM Ltd | Hospitality | 2025 |
| SPW Property Developments Ltd | Real estate | 2021 |
| Squiffy Dog Ltd | Construction | 2015 |
| Sriay Esha Ltd | Wholesale & retail | 2025 |
| Srivignesa Limited | Hospitality | 2023 |
| SSH Commercial Ltd | Real estate | 2023 |
| SSH Holdings Ltd | Extraterritorial | 2016 |
| SSH Investments Limited | Construction | 2012 |
| ST Davids Park Developments Ltd | Construction | 2017 |
| ST. Patricks Day Development Limited | Real estate | 2004 |
| Standbanner Limited | Professional & scientific | 2015 |
| Station Road (Port Talbot) Ltd | Construction | 2025 |
| Station Vape SW Ltd | Wholesale & retail | 2025 |
| Staycations-Cymru CYF | Real estate | 2020 |
| Steel Line Design Ltd | Professional & scientific | 2015 |
| Steel Town Coffee Company Ltd | Hospitality | 2022 |
| Steel Town Windows and Doors Ltd | Construction | 2025 |
| Steen Johns Consulting Ltd | Professional & scientific | 2015 |
| Stella Care Tech Limited | Information & communication | 2021 |
| Stephen Jones Builders Limited | Construction | 2018 |