| S E Roofing and Building Services Ltd | Construction | 2026 |
| S J Griffiths & SON Tipper Hire Ltd | Water & waste | 2017 |
| S Marsh Asset Management Ltd | Financial services | 2018 |
| S Thomas Properties Ltd | Real estate | 2020 |
| S&A Builders & Sons Limited | Construction | 2019 |
| S&C Electric Emea Ltd | Construction | 2008 |
| S&G Recycling Ltd | Water & waste | 2021 |
| S&S Taxi and Minibus Ltd | Transport & logistics | 2023 |
| S.A.G Roofing Bristol Ltd | Construction | 2023 |
| S.T.I. Limited | Real estate | 1974 |
| SA1 Equity Limited | Real estate | 2017 |
| SA10 Ltd | Hospitality | 2026 |
| SAD MAN Limited | Financial services | 2019 |
| Saeed Barber (Briton Ferry) Ltd | Other services | 2025 |
| Safety Letter Box Company Limited | Manufacturing | 1986 |
| Sagacious Skin Limited | Other services | 2017 |
| Sage Rentals Ltd | Real estate | 2020 |
| Salon Xclusive.Co.Uk Limited | Other services | 2011 |
| Salus Property Limited | Health & social care | 2020 |
| Sam's Grooming Room Limited | Other services | 2023 |
| Same Solutions Ltd. | Administrative & support | 2012 |
| Sandokan Consultancy Limited | Information & communication | 2015 |
| Sandra Evans Accountancy Services Ltd | Professional & scientific | 2011 |
| Sandre Group Limited | Wholesale & retail | 2003 |
| Sandvik Osprey Limited | Manufacturing | 1974 |
| Sapphire Transport Services Ltd | Administrative & support | 2025 |
| SB Decorators Limited | Construction | 2013 |
| SBL Retail Limited | Wholesale & retail | 2019 |
| Sccd Properties Ltd | Real estate | 2024 |
| Schofield Trading Limited | Real estate | 2024 |
| Scott's Timber Limited | Wholesale & retail | 2016 |
| SCR Ponds & Landscaping Ltd | Administrative & support | 2026 |
| SE Fabrications Limited | Manufacturing | 2021 |
| Sean Griffiths Limited | Financial services | 2022 |
| Searaven Global Corp Ltd | Professional & scientific | 2018 |
| Sears Property Management Limited | Real estate | 2006 |
| Securus Property Compliance Limited | Professional & scientific | 2015 |
| SEH Education Consultants Ltd | Education | 2019 |
| Select Accident Repair Centre Limited | Wholesale & retail | 2014 |
| Select Local BUS Services Limited | Transport & logistics | 2025 |
| Select MOT and Tyre Centre Limited | Wholesale & retail | 2023 |
| Selj Limited | Professional & scientific | 2010 |
| Sellyourcartoday.Com Ltd | Wholesale & retail | 2021 |
| Sensitive Water Solutions Swim School Limited | Arts & recreation | 2010 |
| Seren Building Solutions Limited | Construction | 2007 |
| Seren Computer Systems Limited | Information & communication | 1986 |
| Seren Environmental Consulting Ltd | Professional & scientific | 2002 |
| Seven Sister Kebab & Pizza Ltd | Hospitality | 2026 |
| Seven Sisters Onllwyn AFC Ltd | Arts & recreation | 2024 |
| Seven Sisters R F C Limited | Arts & recreation | 2017 |
| Seven Sisters Sawmills (Sheds) Limited | Manufacturing | 1999 |
| Seven Sisters Stores Ltd | Wholesale & retail | 2018 |
| SGR Electrical Soloutions Ltd | Construction | 2024 |
| SH Statistical Programming Ltd | Professional & scientific | 2020 |
| Shadow Grassroots CIC | Administrative & support | 2025 |
| Shadow Spirits Ltd | Wholesale & retail | 2023 |
| Shalom Foods Ltd | Hospitality | 2025 |
| Shane Callaghan Ltd | Information & communication | 2026 |
| Share Shape Limited | Hospitality | 2017 |
| Sharmila Consultancy Services Limited | Health & social care | 2022 |
| Sharmila Property Limited | Real estate | 2024 |
| Shepherd Security Ltd | Administrative & support | 2023 |
| Shield Security Service Ltd | Administrative & support | 2007 |
| Shillingfords Fish & Chips Ltd | Hospitality | 2025 |
| Shirlan Construction Limited | Construction | 2004 |
| Short Consultants Ltd | Professional & scientific | 2018 |
| Siesta Group Limited | Manufacturing | 1988 |
| Siesta Paragon Limited | Information & communication | 2022 |
| SIGMA8 Solutions Limited | Manufacturing | 2020 |
| Signature Carpentry Limited | Construction | 2023 |
| Signature Sports Management and Consultancy Ltd | Arts & recreation | 2020 |
| Sileo Consultancy Limited | Administrative & support | 2020 |
| Silurian Publishing Ltd | Information & communication | 2023 |
| Silver Lining Care Ltd | Health & social care | 2020 |
| Silverseal Glass and Glazing Company Limited | Manufacturing | 1991 |
| SIMAIR737 Limited | Arts & recreation | 2017 |
| Simplex FX Limited | Education | 2025 |
| Sims Developments Ltd | Construction | 2026 |
| SIW Eco Energy Ltd | Construction | 2008 |
| Sixty Sixty (Merthyr Tydfil) Limited | Real estate | 2000 |
| Sjpm LLP | | 2018 |
| Skelton-Thomas Engineering Limited | Manufacturing | 1989 |
| Skewen Anglers Club Limited | Agriculture & fishing | 2025 |
| Skewen Building Ltd | Construction | 2024 |
| Skewen Community Leisure Limited | Arts & recreation | 2025 |
| Skewen Hand Car Wash Ltd | Other services | 2019 |
| Skewen Joinery Services Co Ltd | Manufacturing | 2003 |
| Skewen Press Limited(The) | Administrative & support | 1962 |
| Skewen Rugby Football Club Limited | Arts & recreation | 2016 |
| Skye Couriers Limited | Transport & logistics | 2013 |
| Skyline Dream Ltd | Hospitality | 2023 |
| Skyu Ltd | Real estate | 2024 |
| SLE ( Wales ) Limited | Arts & recreation | 2018 |
| Sledge Brick & Block Work Ltd | Construction | 2025 |
| Smashed Patty Ltd | Hospitality | 2025 |
| Smiley Kitchens Ltd | Wholesale & retail | 2017 |
| Smjames Property Ltd | Real estate | 2023 |
| Smless. Limited | Wholesale & retail | 2025 |
| Snows Construction (1976) Limited | Construction | 1976 |
| SO Modular Ltd | Manufacturing | 2016 |