| Reuben Mulenga Ltd | Information & communication | 2023 |
| Revaya Limited | Wholesale & retail | 2025 |
| Revive Wellbeing Collective Limited | Health & social care | 2026 |
| Revive Wellness Cowbridge Ltd | Arts & recreation | 2024 |
| RGM Wealth Management Limited | Financial services | 2019 |
| Rhiwbina Rental Limited | Real estate | 2020 |
| RHP Merchants and Construction Limited | Construction | 2006 |
| Rhys-Jones Consultancy Limited | Information & communication | 2007 |
| Rhythm Creations Ltd | Arts & recreation | 2024 |
| Richard Clarke Health & Fitness Limited | Arts & recreation | 2019 |
| Richard Johns Associates Ltd | Professional & scientific | 2024 |
| Richard Penn Consultancy Limited | Administrative & support | 2007 |
| Richard Whitaker Architects Ltd | Professional & scientific | 2011 |
| Richmond House (Penarth) Limited | Real estate | 2024 |
| Ripple Marketing Consultancy Ltd | Professional & scientific | 2020 |
| Rise Recruitment Group Ltd | Administrative & support | 2024 |
| RLK Design Ltd | Professional & scientific | 2023 |
| RMA Contempo Limited | Real estate | 2022 |
| Road Safety Designs Limited | Professional & scientific | 2014 |
| ROB and VNY Rental Properties Ltd | Health & social care | 2022 |
| Robert Mead HR Services Ltd | Professional & scientific | 2016 |
| Rocket Legal Services Limited | Professional & scientific | 2015 |
| Rokman Ltd | Wholesale & retail | 2020 |
| Romeo's Investments Limited | Real estate | 2021 |
| Ronsons Developments Limited | Real estate | 1981 |
| Ronsons Limited | Administrative & support | 1937 |
| Ronsons Rentals Limited | Real estate | 2016 |
| Roso Digital Ltd | Professional & scientific | 2023 |
| Rough CUT Media Ltd | Information & communication | 2020 |
| Rowing Aviron Remo Rudern Roeien Canottaggio UN Limited | Education | 2018 |
| Royal Buildings (Penarth) Management Company Limited | Real estate | 2007 |
| RPM Engineering Services South Wales Ltd | Professional & scientific | 2010 |
| RS Cars Online Ltd | Wholesale & retail | 2024 |
| RSJ Property Management Ltd | Construction | 2019 |
| Rsob Ltd | Health & social care | 2022 |
| RTB Aesthetics & Wellbeing Ltd | Other services | 2025 |
| Rtrt Consulting Limited | Professional & scientific | 2017 |
| Ruby Arch Properties Limited | Real estate | 2018 |
| Rude Health Ltd | Arts & recreation | 2019 |
| Rwalabs Group Ltd | Information & communication | 2026 |
| S&G Robson Properties Ltd | Real estate | 2024 |
| S&L Electrical Services Ltd | Construction | 2018 |
| S&S Sully Ltd | Hospitality | 2023 |
| S.C. Reversions Limited | Households | 1985 |
| S.H. Dodd & Sons Limited | Real estate | 1963 |
| Saagor Cuisine Limited | Hospitality | 2024 |
| Saavi Ltd | Wholesale & retail | 2020 |
| Sabs Social Work Consulting Ltd | Health & social care | 2025 |
| Sadler Carpentry Limited | Construction | 2026 |
| Sadler Recruitment Ltd | Administrative & support | 2020 |
| SAE Web Development Limited | Professional & scientific | 2015 |
| Safehavencardiff Ltd | Real estate | 2025 |
| Safety and Loss Prevention Services Ltd | Professional & scientific | 2010 |
| SAM Gibson Productions Limited | Arts & recreation | 2006 |
| SAM Johnson Art Limited | Arts & recreation | 2019 |
| Sampson Carpentry and Build Limited | Construction | 2026 |
| Sampson Property Group Ltd | Real estate | 2025 |
| Saneemal Ltd | Health & social care | 2023 |
| Sarah Alice Jones Design Ltd | Information & communication | 2024 |
| SAV Holding Management Limited | Real estate | 2025 |
| Scaffolduk Ltd | Construction | 2023 |
| Scale With DAN Limited | Education | 2023 |
| Scdp Ventures Ltd | Real estate | 2019 |
| Scene Smart Ltd | Construction | 2017 |
| School Website Design Agency Limited | Information & communication | 2019 |
| Scott Elias Tutoring LLP | | 2024 |
| Scotton Lorimer Group Ltd | Real estate | 2025 |
| Scrase Properties Ltd | Real estate | 2016 |
| Screen Craft Guild CYF. | Other services | 2026 |
| SCS Aftercare Limited | Other services | 2008 |
| Sculpta Fitness Ltd | Wholesale & retail | 2024 |
| Seabank Management 2001 Limited | Households | 2001 |
| Seabay Nautical Ltd | Information & communication | 2016 |
| Seaforth Learning Services Limited | Education | 2007 |
| Seakit Ltd | Wholesale & retail | 2017 |
| Sealed Consult Ltd | Professional & scientific | 2022 |
| Searchlight Global Ltd | Wholesale & retail | 2020 |
| Seco-Sol Limited | Wholesale & retail | 2013 |
| Securestart Residents Management Limited | Real estate | 1986 |
| Seebalt Ltd | Professional & scientific | 2014 |
| Self Admin Limited | Wholesale & retail | 2021 |
| September Born Films Limited | Information & communication | 2009 |
| Seren Vale Ltd | Manufacturing | 2025 |
| Shadowboximaging Ltd | Health & social care | 2024 |
| Shant Consulting Limited | Information & communication | 2015 |
| Shashco Ltd | Health & social care | 2023 |
| Shear Testing Systems Limited | Professional & scientific | 2021 |
| Shed Pickups Ltd | Manufacturing | 2023 |
| Shelfco 20 Limited | Extraterritorial | 2020 |
| Shona Health Limited | Health & social care | 2017 |
| Shopedevs Ltd | Wholesale & retail | 2026 |
| Shore Penarth Ltd | Wholesale & retail | 2014 |
| Siame Limited | Real estate | 2022 |
| Sian Grigg Limited | Administrative & support | 2010 |
| Siffat Ltd | Wholesale & retail | 2026 |
| Sign School Ltd | Education | 2022 |
| Sign Services (Posters) Ltd | Manufacturing | 2026 |
| Signal Design Group Ltd | Financial services | 2025 |
| Silures Penarth Limited | Hospitality | 2025 |
| Silver Arch Properties Limited | Real estate | 2013 |