| Sharks HQ Limited | Wholesale & retail | 2026 |
| Sharks Swim Shop Ltd | Wholesale & retail | 2014 |
| Sharosy Enterprises Ltd | Hospitality | 2024 |
| Sharpes Court (Management) Limited | Extraterritorial | 2003 |
| Sharpest Marketing Limited | Professional & scientific | 2025 |
| Shathanaa's Property Ltd | Real estate | 2024 |
| Shaun James Catering Services Limited | Hospitality | 2019 |
| Shaws (Cardiff) Limited | Wholesale & retail | 1951 |
| Shazam Liquidation Stock Ltd | Wholesale & retail | 2014 |
| SHC Textiles Limited | Professional & scientific | 2011 |
| SHC2024 Limited | Arts & recreation | 2024 |
| SHE Runs This City Ltd | Arts & recreation | 2025 |
| Sheds N Chalets Limited | Manufacturing | 2002 |
| Sheep Ford Ltd | Real estate | 2018 |
| Shepherd Homes Agency Ltd | Real estate | 2020 |
| Shepherd's Barn Ltd | Arts & recreation | 2021 |
| Shepherds of Gower Ltd | Wholesale & retail | 2019 |
| Sheriffs Biltong Ltd | Manufacturing | 2024 |
| Sherman and Sherman Holdings Ltd | Financial services | 2026 |
| Sherwood Florist Limited | Wholesale & retail | 2009 |
| Shield Risk Services (UK) Limited | Administrative & support | 2012 |
| Shield Security Limited | Public administration | 1997 |
| Shigoto Kaizen Ltd | Health & social care | 2023 |
| Shiji's Boutique Ltd | Wholesale & retail | 2024 |
| Shine Cymru Life Skills Services Ltd | Health & social care | 2017 |
| Shinwarrior Limited | Professional & scientific | 2017 |
| Ship Inn (Swansea 2019) Limited | Hospitality | 2019 |
| Shipmax Ltd | Information & communication | 2023 |
| Shir & Sons Traders Ltd | Wholesale & retail | 2015 |
| Shiraz Turkish Grill Ltd | Hospitality | 2020 |
| Shirt Happens Limited | Wholesale & retail | 2026 |
| Shirui International Ltd | Wholesale & retail | 2020 |
| Shisha Castle Ltd | Other services | 2025 |
| Shivaay Swansea Ltd | Wholesale & retail | 2025 |
| Shkak Barber Ltd | Other services | 2025 |
| Shockwave Connect Ltd | Information & communication | 2025 |
| Shockwave Digital Ltd | Information & communication | 2013 |
| Shoe Dog Investments Limited | Financial services | 2023 |
| Shopping UN Limited | Extraterritorial | 2023 |
| Shorebase Logistics Limited | Administrative & support | 2009 |
| Shorebreak Ltd | Real estate | 2009 |
| Shoreline Cleaning Services Ltd | Administrative & support | 2023 |
| Shoreline Mumbles Ltd | Hospitality | 2022 |
| Short Bark & Sides Dog Grooming and Day Care Ltd | Other services | 2019 |
| Shorts Accident Repair Centre Limited | Transport & logistics | 2005 |
| Shorts Auto Electrical (Swansea) Ltd | Wholesale & retail | 1970 |
| Shotblue Limited | Real estate | 1995 |
| Shotview Limited | Construction | 1995 |
| Shotwick Land Limited | Construction | 2016 |
| Shouly Enterprises One Limited | Hospitality | 2013 |
| Show Support Services Limited | Administrative & support | 2005 |
| Showdown Cards Ltd | Wholesale & retail | 2025 |
| SHS Property Maintenance Ltd | Construction | 2024 |
| Shufa Property Services Ltd | Real estate | 2024 |
| Shumai Chinese Limited | Hospitality | 2021 |
| Shunfa Burner Ltd | Administrative & support | 2023 |
| SHY Sheep Distillery Limited | Manufacturing | 2025 |
| SI & GI Ltd | Health & social care | 2025 |
| Siamic Limited | Other services | 2019 |
| Sian Batcup PMU Ltd | Health & social care | 2024 |
| Sian Mcgill Limited | Arts & recreation | 2020 |
| Sian Properties Ltd | Real estate | 2016 |
| Sicaran Design Services Limited | Professional & scientific | 2025 |
| Sick INK Tattoos and Piercings Limited | Other services | 2023 |
| Sick Prints Ltd | Manufacturing | 2025 |
| SID and Dina Ltd | Professional & scientific | 2017 |
| SID Martin Property Limited | Real estate | 2017 |
| Sidorenko & Co. Limited | Manufacturing | 2025 |
| Sieffre Services Ltd | Professional & scientific | 2011 |
| SIG Industrial Solutions Ltd | Construction | 2003 |
| Sigga Design Limited | Information & communication | 2003 |
| Sign and Print Systems Ltd | Manufacturing | 2017 |
| Sign Bros. Ltd | Manufacturing | 2025 |
| Sign Property Ltd | Administrative & support | 2022 |
| Signal House Advertising Limited | Hospitality | 2018 |
| Signature Building and Maintenance Ltd | Construction | 2019 |
| Signature Groundworks Ltd | Construction | 2021 |
| Signature Homes and Developments Limited | Construction | 2016 |
| Signature Skin Ltd | Other services | 2021 |
| Signature Spaces Swansea Ltd | Real estate | 2024 |
| Signature Support Ltd | Health & social care | 2020 |
| Signum Motors Ltd | Manufacturing | 2025 |
| Signum Property Ltd | Real estate | 2025 |
| Silas Ministries | Professional & scientific | 2024 |
| Silbar Hospitality Limited | Hospitality | 2019 |
| Sileo Holdings Ltd | Financial services | 2026 |
| Silicon Consulting Limited | Professional & scientific | 2022 |
| Silicon Mafia Limited | Information & communication | 2022 |
| Silkworm Systems Ltd | Information & communication | 2026 |
| Silver Acorn Limited | Manufacturing | 1969 |
| Silver Bullet Branding Limited | Professional & scientific | 2019 |
| Silver Ocean Limited | Hospitality | 2018 |
| Silver Tears Limited | Other services | 2021 |
| Silverline Trading UK Limited | Wholesale & retail | 2002 |
| Silvermarsh Limited | Financial services | 2017 |
| Silvermetric Limited | Information & communication | 2005 |
| Simerenya Consulting Ltd | Professional & scientific | 2023 |
| Simkova, Bergstein & Baez Lawyers Limited | Financial services | 2020 |
| Simmonds Carpentry & Joinery Ltd | Manufacturing | 2008 |
| Simoma Ltd | Professional & scientific | 2024 |