| Skygrid Surveys Ltd | Professional & scientific | 2026 |
| Skyla Properties Limited | Financial services | 2023 |
| Skyline Logistic Services Ltd | Transport & logistics | 2026 |
| Skyline Swansea Limited | Arts & recreation | 2022 |
| SKYLINEPROPERTY1 Ltd | Hospitality | 2024 |
| Skysea Caravan Site Limited | Wholesale & retail | 2020 |
| Skysill Exterior Cleaning Ltd | Administrative & support | 2026 |
| Skyward Design Studio Ltd | Other services | 2013 |
| Skywash Drones (Wales-Uk) Limited | Administrative & support | 2025 |
| SL Films Ltd | Information & communication | 2025 |
| Slabcrest Limited | Households | 1979 |
| Slade's Accident Repair Centre Ltd | Wholesale & retail | 2023 |
| Slateform Residents Association Limited | Hospitality | 1983 |
| Sleek Accommodations Limited | Real estate | 2024 |
| Sleek IT Solutions Limited | Information & communication | 2024 |
| Sleep Easy Swansea Limited | Hospitality | 2016 |
| SLH Capital Limited | Administrative & support | 2015 |
| Slh-Uk Limited | Wholesale & retail | 2019 |
| Slice and Dice (Pontardawe) Limited | Hospitality | 2012 |
| Slice of Paradise Ltd | Wholesale & retail | 2026 |
| Slix Salon Limited | Other services | 2019 |
| Sloboda Ltd | Real estate | 2025 |
| Sloth Mumbles Limited | Hospitality | 2025 |
| Sloth Swansea Limited | Hospitality | 2022 |
| Slow Sundays Ltd | Wholesale & retail | 2024 |
| SLR Developments Limited | Construction | 2014 |
| SLR Finance Limited | Professional & scientific | 2025 |
| Slurp Noodles Limited | Hospitality | 2023 |
| SM Recovery Ltd | Transport & logistics | 2022 |
| SM Restaurants Ltd | Hospitality | 2021 |
| Small Biotechnologies Ltd | Professional & scientific | 2020 |
| Small Chops Treats Ltd | Hospitality | 2025 |
| Smarks Ltd | Wholesale & retail | 2000 |
| Smart Anchor Capital LLP | | 2016 |
| Smart Assessment and Management Ltd | Information & communication | 2026 |
| Smart Assure Finance Ltd | Financial services | 2025 |
| Smart Builders Swansea Ltd | Construction | 2025 |
| Smart Deliveriez Limited | Hospitality | 2020 |
| Smart Order Management Ltd | Information & communication | 2021 |
| Smart Therapeutics Ltd | Professional & scientific | 2016 |
| Smart Website Designers Ltd | Information & communication | 2019 |
| SMART-D-1982 Ltd | Transport & logistics | 2020 |
| Smartliving Installation Ltd | Manufacturing | 2023 |
| Smartsan UK Ltd | Wholesale & retail | 2019 |
| Smartstream Renewable Technologies Ltd | Professional & scientific | 2025 |
| Smash Monkey Productions Ltd | Hospitality | 2025 |
| SMD Capital Limited | Professional & scientific | 2018 |
| Smf.Independent Social Work Ltd | Health & social care | 2023 |
| Smile and Stretch Yoga Ltd | Other services | 2025 |
| Smile Materials Limited | Manufacturing | 2010 |
| Smile Plastics Limited | Manufacturing | 2019 |
| Smiles by DAN Ahmed Limited | Health & social care | 2023 |
| Smith & Mill Furniture Ltd | Manufacturing | 2017 |
| Smith Aerospace Consultancy Limited | Professional & scientific | 2025 |
| Smith Llewelyn Limited | Professional & scientific | 2001 |
| Smith's Joinery and Building Contractors Limited | Construction | 2019 |
| Smithmartin Partnership LLP | | 2005 |
| Smiths @ 141 Limited | Hospitality | 2022 |
| Smiths Property Agent Ltd | Real estate | 2020 |
| Smiths Sales and Lettings Ltd | Real estate | 2015 |
| Smithson Gallery Limited | Arts & recreation | 2009 |
| Smjh Limited | Professional & scientific | 2010 |
| SMK Plumbing and Heating Limited | Construction | 2014 |
| Smka Ltd | Professional & scientific | 2025 |
| Smooch Aesthetics Specialists Limited | Health & social care | 2022 |
| Smoothas Ltd | Health & social care | 2016 |
| Smqs Consultancy Limited | Professional & scientific | 2019 |
| SMS 4 U Limited | Hospitality | 2019 |
| Smst Construction and Property Ltd | Real estate | 2025 |
| Smtx Ltd | Financial services | 2024 |
| SMU Global Education Limited | Education | 2018 |
| Smugglers Gift Shop Limited | Wholesale & retail | 2012 |
| SMZ & Sons Ltd | Wholesale & retail | 2022 |
| SN Aesthetics Limited | Other services | 2025 |
| SN Luxury Car Hire Ltd | Administrative & support | 2025 |
| SNA Management Ltd | Wholesale & retail | 2024 |
| Snap & Serve Ltd | Wholesale & retail | 2025 |
| Snell Family Holdings Ltd | Financial services | 2026 |
| Snoop Vape Shop NO 1 Limited | Wholesale & retail | 2023 |
| Snow Prop Ltd | Households | 2025 |
| Snowdon Enterprise Consultancy Company Ltd | Professional & scientific | 2020 |
| Snowslippers International Limited | Administrative & support | 2012 |
| Snowslippers Limited | Administrative & support | 2005 |
| SO Barista School Limited | Education | 2025 |
| SO Fit Health and Wellbeing CIC | Other services | 2022 |
| So-Kleen Ltd | Administrative & support | 2025 |
| Social AID Trust | Education | 2017 |
| Social Enterprise East Midlands Limited | Professional & scientific | 2017 |
| Social Firms Wales Limited | Administrative & support | 2005 |
| Socialdice UK Limited | Hospitality | 2021 |
| Socialuxe Ltd | Professional & scientific | 2025 |
| Socket Sense Ltd | Professional & scientific | 2025 |
| SOE MOE and Daughters Limited | Health & social care | 2016 |
| SOF Technical Ltd | Professional & scientific | 2024 |
| Sofa Moods Limited | Manufacturing | 2026 |
| Sofit Group Ltd | Education | 2020 |
| Sofra Swansea Ltd | Wholesale & retail | 2023 |
| Soft Slab Ltd | Wholesale & retail | 2026 |
| Soft Tech Consulting Limited | Information & communication | 2018 |
| Softell Ltd | Information & communication | 2019 |