| C&G Mechanical Limited | Construction | 2012 |
| C&H Cardiff Limited | Hospitality | 2025 |
| C&J Medtech Ltd | Information & communication | 2021 |
| C&J Properties (NE) Limited | Hospitality | 2019 |
| C&J Spaces Ltd | Hospitality | 2019 |
| C&K Automotive Services Limited | Transport & logistics | 2017 |
| C&L Property Services Limited | Real estate | 2025 |
| C&M Clinical Engineering Solutions Ltd | Manufacturing | 2020 |
| C&M Development and Design Limited | Construction | 2022 |
| C&M Property Plan Limited | Real estate | 2019 |
| C&M Site Services Ltd. | Construction | 2015 |
| C&M Specialist Installations Limited | Construction | 2023 |
| C&R Global Ltd | Wholesale & retail | 2022 |
| C&S Civils Ltd | Construction | 2017 |
| C&W Limited | Hospitality | 2026 |
| C-43 Ltd | Financial services | 2016 |
| C-Levelresumes Ltd | Information & communication | 2023 |
| C-Vista Ltd | Information & communication | 2006 |
| C.& J.Hirst & Sons,Limited | | 1895 |
| C.A.B. Heating & Plumbing Limited | Manufacturing | 2009 |
| C.A.M. Motors Limited | Wholesale & retail | 2005 |
| C.C. Distribution Limited | | 1986 |
| C.Collard Construction Ltd | Construction | 2020 |
| C.G & Sons Ltd | Construction | 2017 |
| C.I.Mykes Ltd | Information & communication | 2018 |
| C.I.S. (Cardiff) Limited | Financial services | 2014 |
| C.Jal Limited | Wholesale & retail | 2023 |
| C.P Cafe Restaurant Ltd | Hospitality | 2018 |
| C.R. Engl Holdings Limited | Financial services | 1978 |
| C.R.H. (Balaia) Limited | Households | 1989 |
| C.S Roofing and Building Ltd | Construction | 2026 |
| C.T.F Developments Limited | Real estate | 2025 |
| C.V.S Specialist Recovery and Inspections Ltd | Transport & logistics | 2026 |
| C09 & C10 at Cathedral Gardens Ltd | Real estate | 2022 |
| C1 Performance Ltd | Wholesale & retail | 2019 |
| C10UD Ltd | Wholesale & retail | 2025 |
| C2020 Ltd | Administrative & support | 2020 |
| C2C Healthcare Limited | Health & social care | 2015 |
| C2C Market Ltd | Wholesale & retail | 2024 |
| C2DEVELOPERS Ltd | Information & communication | 2025 |
| C3 123 Limited | Financial services | 2020 |
| C3 456 Limited | Financial services | 2020 |
| C3 789 Limited | Financial services | 2020 |
| C3 Clinics LLP | | 2022 |
| C3 P&M Limited | Real estate | 2000 |
| C5 Networks Ltd | Construction | 2019 |
| C6 Consultancy Ltd | Professional & scientific | 2021 |
| CA2SAPROPERTYGROUP Ltd | Hospitality | 2025 |
| Caad Shop Ltd | Wholesale & retail | 2017 |
| Caas Trading Company Limited | Other services | 2013 |
| CAB Drive Rentals Ltd | Transport & logistics | 2023 |
| CAB Solutions Ltd | Administrative & support | 2017 |
| Cabecou Investments Limited | Information & communication | 2012 |
| Cabinco Structures Limited | Manufacturing | 2015 |
| Cabinet Farming Ltd | Manufacturing | 2021 |
| Cabology Ltd | Transport & logistics | 2019 |
| Cabrequest Ltd | Administrative & support | 2023 |
| CAC Global Enterprise Ltd | Education | 2020 |
| Cache London Ltd | Information & communication | 2019 |
| Cactus Design Limited | Arts & recreation | 2003 |
| Cactus Renovations Ltd | Construction | 2026 |
| Cadair Goch CYF. | Arts & recreation | 2025 |
| Cadamier Ltd | Professional & scientific | 2022 |
| Cadarn Consulting Ltd. | Professional & scientific | 2002 |
| Cadarn Property Maintenance Ltd | Construction | 2026 |
| Cadbury and Jones Ltd | Professional & scientific | 2014 |
| Caden Scaffolding Contracts Limited | Construction | 2017 |
| Cadena Investments Limited | Financial services | 2024 |
| Cadfan Group UK Ltd | Construction | 2024 |
| Cadlot Developments Ltd | Construction | 2016 |
| Cadlot Healthcare Ltd | Health & social care | 2025 |
| Cadlot Ltd | Health & social care | 2014 |
| Cadmium Aero Limited | Professional & scientific | 2026 |
| Cadmon Intellectual Property Co., Ltd. | Extraterritorial | 2019 |
| Cadno Accounting Ltd | Professional & scientific | 2014 |
| Cadno Media Ltd | Information & communication | 2024 |
| Cadogan House (Cardiff Bay) Management Company Limited | Households | 2017 |
| Cadogan Mcqueen Concierge Limited | Real estate | 2016 |
| Cadremont Limited | Manufacturing | 2009 |
| Cadrive Ltd | Administrative & support | 2024 |
| Cadtech-Design Ltd | Professional & scientific | 2019 |
| Caduceus Trade Limited | Information & communication | 2026 |
| Cadvis Limited | Information & communication | 2009 |
| Cadwallader Home Solutions Limited | Construction | 2011 |
| Cadwynbloc Ltd | Information & communication | 2025 |
| Cae-Glas Homes Ltd | Real estate | 2025 |
| Caedelyn Maintenance Service Limited | Households | 1961 |
| Caelaira Ltd | Information & communication | 2025 |
| Caer Capital Limited | Financial services | 2021 |
| Caer IFA Ltd | Financial services | 2025 |
| Caerbhaill Consultancy Ltd | Professional & scientific | 2024 |
| Caerfelin Crwys Road Limited | Construction | 2016 |
| Caerleon Ltd | Real estate | 2024 |
| Caerphilly Cabin and Stone Ltd | Administrative & support | 2025 |
| Caerphilly Hand Car Wash & Valeting Ltd | Other services | 2026 |
| Caerphilly Investments Limited | Real estate | 2005 |
| Caerphilly Jade Ltd | Hospitality | 2018 |
| Caerphilly Kebabs Limited | Hospitality | 2020 |
| Caerphilly Print Services Limited | Manufacturing | 2023 |
| Caerphilly Vape Shop Ltd | Wholesale & retail | 2025 |