| Cashin Developments Ltd | Real estate | 2019 |
| Cashin Holdings Ltd | Real estate | 2021 |
| Cashless Payments Ltd | Information & communication | 2022 |
| Cashup Ltd | Financial services | 2015 |
| Casinex Consultancy Ltd | Information & communication | 2019 |
| Casita Group Limited | Real estate | 2018 |
| Cask Group Ltd | Wholesale & retail | 2021 |
| Cask Spirits Global Limited | Wholesale & retail | 2024 |
| Caskaway Taverns Ltd | Real estate | 2015 |
| Casongh Ltd | Professional & scientific | 2022 |
| Casoras | Professional & scientific | 2025 |
| Caspian Feast Ltd | Wholesale & retail | 2025 |
| Caspian International Trading Co., Ltd | Wholesale & retail | 2021 |
| Caspian Law and Education Ltd | Education | 2025 |
| Caspian Sterling Ltd | Professional & scientific | 2024 |
| Caspiana Limited | Construction | 2006 |
| Cass Property Solutions Ltd | Households | 2025 |
| Cass Scaffolding Limited | Wholesale & retail | 2008 |
| Cassam Property Ltd. | Real estate | 2015 |
| Cassley Autocare Ltd | Wholesale & retail | 2015 |
| Cassley Properties Ltd | Real estate | 2024 |
| Castara Law Limited | Professional & scientific | 2006 |
| Castaservice Limited | Transport & logistics | 2025 |
| Castell Cards Limited | | 1982 |
| Castell Coffee Ltd | Hospitality | 2022 |
| Castell CYF | Financial services | 1997 |
| Castell Lets Ltd | Real estate | 2025 |
| Castenia Trading PC | | 2018 |
| Castillo Property Development Ltd | Construction | 2025 |
| Castle Bridal Limited | Wholesale & retail | 2016 |
| Castle Combe Exhibitions Ltd | Arts & recreation | 2003 |
| Castle Court Freehold Limited | Other services | 2004 |
| Castle Energy Services Limited | Construction | 1993 |
| Castle Health Limited | Health & social care | 2007 |
| Castle Hill Court (ST. Fagans) Maintenance Limited | Households | 1969 |
| Castle Investment Group Limited | Real estate | 2025 |
| Castle Nails 6 Ltd | Other services | 2023 |
| Castle Orientation Holding Corporation Ltd | Information & communication | 2022 |
| Castle Precision Services Ltd | Administrative & support | 2017 |
| Castle Properties (Cardiff) Limited | Real estate | 1962 |
| Castle Property & Services LLP | | 2020 |
| Castle Property and Services Ltd | Real estate | 2021 |
| Castle Radiators Ltd | Wholesale & retail | 2023 |
| Castle Rook Limited | Professional & scientific | 2015 |
| Castle Vale Displays Limited | Manufacturing | 2019 |
| Castle View B & B Limited | Hospitality | 2020 |
| Castle View Property Development Ltd | Real estate | 2018 |
| Castlebridge Investments Limited | Real estate | 1999 |
| Castlebridge Risk Solutions Ltd | Financial services | 2025 |
| Castlefields(Gallows Hill) Management Company Ltd | Real estate | 2025 |
| Castleridge Center Ltd | Health & social care | 2026 |
| Castlesproperties Ltd | Households | 2019 |
| Castlestone Construction Limited | Construction | 2019 |
| Castleton Property Holdings Limited | Real estate | 2024 |
| Castleview Accountancy Limited | Professional & scientific | 2011 |
| Castleview Payroll Services Limited | Professional & scientific | 2016 |
| Castlewood Consultancy Ltd | Professional & scientific | 2023 |
| Castro Music Ltd | Extraterritorial | 2017 |
| Casualty Management Limited | Information & communication | 2023 |
| Caswell Bay Holdings Ltd | Real estate | 2024 |
| Cat and Bear Studio Ltd | Arts & recreation | 2017 |
| Cat DAL Interiors Ltd | Professional & scientific | 2019 |
| Cat DRY Ltd | Manufacturing | 2025 |
| Cata PP Ltd | Wholesale & retail | 2025 |
| Cataf Ltd | Wholesale & retail | 2025 |
| Catalyst in Communities C.I.C. | Health & social care | 2011 |
| Catalyst Inno Limited | Professional & scientific | 2019 |
| Catalyst Investment Property Limited | Construction | 2025 |
| Catalytic Consultancy Limited | Professional & scientific | 2018 |
| Catch and Kebab Ltd | Hospitality | 2025 |
| Catch Crispy Fish and Chips Ltd | Hospitality | 2024 |
| Catchas Limited | Professional & scientific | 2018 |
| Catchtech Ltd | Wholesale & retail | 2023 |
| Catchy Clouds Limited | Wholesale & retail | 2025 |
| Caterar Limited | Wholesale & retail | 2017 |
| Catering Dynamics Ltd | Hospitality | 2022 |
| Catering Group Company Two Limited | Hospitality | 2025 |
| Catering Group Limited | Hospitality | 2025 |
| Catering Hub Cardiff Ltd | Wholesale & retail | 2025 |
| Catering UK Wholesale Services Ltd | Wholesale & retail | 2019 |
| Caterlee Limited | Manufacturing | 2020 |
| Caterquip (Nottingham) Ltd | Wholesale & retail | 2015 |
| Catertech Holdings Limited | Financial services | 2019 |
| Catertech Services Limited | Manufacturing | 1995 |
| Cath Delve Consultancy Limited | Education | 2015 |
| Cathalex Ltd | Professional & scientific | 2017 |
| Cathay Energy Ltd | Mining & quarrying | 2016 |
| Cathay Holding Ltd | Other services | 2019 |
| Cathays & Central Youth and Community Project | Education | 2007 |
| Cathays Barber Shop Limited | Other services | 2019 |
| Cathays Bars Ltd | Hospitality | 2022 |
| Cathays Chicken Delight Ltd | Hospitality | 2020 |
| Cathays Developments Limited | Construction | 2012 |
| Cathays Property Ltd | Real estate | 2022 |
| Cathays Vape Limited | Wholesale & retail | 2025 |
| Cathedral 73 Limited | Real estate | 2013 |
| Cathedral Court (Llandaff) Limited | Extraterritorial | 1997 |
| Cathedral Financial Services LLP | | 2003 |
| Cathedral Gardens (Cardiff) Management Company Limited | Households | 2021 |
| Cathedral Gardens Ltd | Real estate | 2018 |