| SI Property Services Ltd | Real estate | 2026 |
| Sian Fisher Ltd | Professional & scientific | 2019 |
| Silver Fern Coaching Ltd | Education | 2020 |
| Sinelab Ltd | Professional & scientific | 2018 |
| Sirhowy Valley Honeybee Company Ltd | Agriculture & fishing | 2014 |
| Site Construction Services Limited | Other services | 2014 |
| SJ Fitness Limited | Arts & recreation | 2024 |
| Skills Training Solutions Limited | Education | 2013 |
| SKILLS4RENEWABLES Ltd | Education | 2022 |
| Skyrunner Limited | Health & social care | 2014 |
| Slice & Spice Pizzeria Ltd | Hospitality | 2025 |
| SMR Rail Ltd | Construction | 2018 |
| Smugglers Tack & Events Limited | Agriculture & fishing | 2019 |
| Sonict Engineering Inspection Ltd | Professional & scientific | 2022 |
| Sourc'D Group Ltd | Wholesale & retail | 2015 |
| South Wales Liquid Screed Limited | Construction | 2019 |
| South Wales Project Properties Limited | Real estate | 2023 |
| South Wales Property Investments Ltd | Real estate | 2020 |
| South Wales Solar and Battery Ltd | Construction | 2022 |
| South Wales Solutions Ltd | Professional & scientific | 2007 |
| South Wales Spine Centre Ltd | Health & social care | 2015 |
| South Wales Suppliers Limited | Wholesale & retail | 2002 |
| Southern Sales Ltd | Wholesale & retail | 2014 |
| Southline Interiors Ltd | Construction | 2025 |
| Spartan Activewear Limited | Wholesale & retail | 2020 |
| SPD Cura Ltd | Real estate | 2022 |
| SPD Motors Ltd | Wholesale & retail | 2022 |
| SPD Property Ltd | Construction | 2018 |
| Speakovation Ltd | Professional & scientific | 2023 |
| Specialised Cladding Systems Ltd | Construction | 2025 |
| Specialised EWI Systems Ltd | Construction | 2023 |
| Spinney Site Welding Ltd | Manufacturing | 2026 |
| Squeaky Cleaned Windows Ltd | Other services | 2014 |
| Squeek and Sparkle Ltd | Other services | 2025 |
| SS Carpentry Ltd | Construction | 2020 |
| ST Davids Service Station Limited | Wholesale & retail | 2009 |
| Staffify UK Ltd | Professional & scientific | 2024 |
| Standard and Specialised Fasteners Limited | Wholesale & retail | 1985 |
| Stanley J. Nicholas Limited | Other services | 1970 |
| Star-Lux Aesthetics Ltd | Health & social care | 2018 |
| Steel Solutions (Wales) Ltd | Manufacturing | 2009 |
| Stellar Carpet & Flooring Ltd | Wholesale & retail | 2020 |
| Stepping Stones Playgroup C.I.C. | Health & social care | 2019 |
| Stormproof Roofing & Building Wales Limited | Construction | 2023 |
| Stowe Homes Ltd | Real estate | 2023 |
| Strap Ltd | Wholesale & retail | 2024 |
| Stratops Consulting Ltd | Professional & scientific | 2026 |
| Street 54 Ltd | Hospitality | 2024 |
| Stuart Bowden Ltd | Professional & scientific | 2021 |
| Studio 54 Blackwood Limited | Arts & recreation | 2019 |
| Stupps Ltd | Wholesale & retail | 2021 |
| Sun Valley Ebbw Vale Limited | Arts & recreation | 2010 |
| Sunnycourt Limited | Health & social care | 2005 |
| Sunrise Rail Limited | Construction | 2024 |
| Sunroofs and Stripes Wales Limited | Wholesale & retail | 1984 |
| Susannah's Homes Management Ltd | Real estate | 2026 |
| Sustainable HR and Safety Solutions Ltd | Professional & scientific | 2019 |
| Sustainable Materials Development Limited | Professional & scientific | 2020 |
| SW Donnies Ltd | Wholesale & retail | 2026 |
| Swift Cars (South Wales) Limited | Wholesale & retail | 2012 |
| Swper Farm Shop Limited | Wholesale & retail | 2024 |
| Synflax Retail Ltd | Wholesale & retail | 2024 |
| Syntech Computer Services Ltd | Information & communication | 2015 |
| Systematic UK Ltd | Manufacturing | 2006 |
| T & C Supplies Limited | Wholesale & retail | 2013 |
| T G Car Sales Limited | Wholesale & retail | 2013 |
| T J Brickwork Limited | Construction | 2022 |
| Tails of Blackwoof Ltd | Arts & recreation | 2024 |
| Tails of Distinction Limited | Professional & scientific | 2018 |
| Taliesin Conservation Limited | Construction | 2009 |
| Tattoos by Whisky Limited | Other services | 2002 |
| Taylour Electrical Ltd | Construction | 2024 |
| TC Recruitment Ltd | Administrative & support | 2015 |
| Tcjt Ltd | Health & social care | 2024 |
| TDH Retail Ltd | Wholesale & retail | 2021 |
| Teamwork ICT Limited | Information & communication | 2016 |
| Technia Business Solutions Limited | Professional & scientific | 2005 |
| Technia Environment and Planning Limited | Professional & scientific | 2014 |
| Teleshore Holdings Ltd | Financial services | 2019 |
| Teleshore U.K. Limited | Manufacturing | 1995 |
| Thaaru Limited | Wholesale & retail | 2017 |
| THE 2ND Spell Limited | Other services | 2002 |
| THE Beer Box Company (Abergavenny) Ltd | Hospitality | 2024 |
| THE Cross Oak Inn PUB Co Ltd | Hospitality | 2021 |
| THE Earning Curve Limited | Professional & scientific | 2012 |
| THE Flora Candle Company Ltd | Wholesale & retail | 2021 |
| THE Floral Edit Limited | Wholesale & retail | 2025 |
| THE Full EV Ltd | Construction | 2022 |
| THE Global Procurement Exchange Limited | Professional & scientific | 2022 |
| THE Haven Aesthetics Limited | Other services | 2023 |
| THE Hawthorns (Wotton) Management Company Limited | Households | 2024 |
| THE Headboard Workshop Ltd | Manufacturing | 2011 |
| THE New Foresters Limited | Hospitality | 2022 |
| THE Old Barn Hill Garage Ltd | Wholesale & retail | 2026 |
| THE Rising Tide Collective Ltd | Information & communication | 2025 |
| THE Social Housing Family CIC | Real estate | 2018 |
| THE Square Caffe Ltd | Hospitality | 2024 |
| THE Square Pizza Blackwood Limited | Wholesale & retail | 2026 |
| THE Square Pizza Co Blackwood Limited | Wholesale & retail | 2026 |
| THE Sunshack (Wales) Limited | Other services | 2011 |