| Cyber Fibre Limited | Information & communication | 2025 |
| Cyber World Defence Technology Limited | Information & communication | 2025 |
| Cybersafeuk Ltd | Information & communication | 2023 |
| Cybervists CIC | Information & communication | 2024 |
| Cycle Solutions (Cycle to Work) Limited | Wholesale & retail | 2006 |
| Cycleworld Limited | Professional & scientific | 2002 |
| Cyden Limited | Manufacturing | 2002 |
| Cyden Skin Wellness Limited | Professional & scientific | 2026 |
| Cyfarth Ltd | Information & communication | 2022 |
| Cyfarwydd Cyfyngedig | Information & communication | 2021 |
| Cyfle I Adeiladu / Chance to Build Ltd | Construction | 2019 |
| Cyfoeth Y Coed C.I.C. | Agriculture & fishing | 2024 |
| Cygnus Data Solutions Ltd | Information & communication | 2022 |
| Cygnus Holdings (Cardiff) Ltd | Construction | 2018 |
| Cygnus Holdings (Gorseinon) Ltd | Real estate | 2025 |
| Cygnus Holdings (Wrexham) Ltd | Other services | 2024 |
| Cygnus Investments Limited | Other services | 2015 |
| Cymorth Kidd CYF | Professional & scientific | 2019 |
| Cymraeg Cwmnu Cyfieithu CYF | Administrative & support | 2024 |
| Cymric & Daughters Ltd | Real estate | 2026 |
| Cymric Holiday Estates Management Limited | Professional & scientific | 1972 |
| Cymru Automation Limited | Administrative & support | 2009 |
| Cymru Coaches Limited | Transport & logistics | 2005 |
| Cymru Coffee Limited | Wholesale & retail | 2001 |
| Cymru Family Pathway Limited | Public administration | 2026 |
| Cymru Guardian Windows Limited | Construction | 2025 |
| Cymru Hydraulics Ltd | Wholesale & retail | 2009 |
| Cymuned Ltd | Information & communication | 2025 |
| Cyngor Rheolaeth Cymru/Wales Management Council | Professional & scientific | 1999 |
| Cypher Analytics Ltd | Information & communication | 2025 |
| Cypright Limited | Professional & scientific | 2013 |
| Cyril Norton & Sons (Plant) Limited | Extraterritorial | 1999 |
| Cyril Price & SON Limited | Real estate | 1958 |
| CZ Investment Ltd. | Real estate | 2015 |
| D & C Electrical (Swansea) Ltd | Construction | 2013 |
| D & D Home Maintenance Solutions Ltd | Construction | 2023 |
| D & E Thomas Property Management Ltd | Real estate | 2022 |
| D & K Carpentry Contractors Limited | Construction | 2010 |
| D & L Construction Limited | Real estate | 2006 |
| D & S Deliveries Limited | Transport & logistics | 2026 |
| D & T Property Developments Limited | Construction | 2008 |
| D and C Taverns Limited | Hospitality | 2026 |
| D and M Griffiths Property Investments Limited | Real estate | 2016 |
| D B N Electrical Ltd | Other services | 2024 |
| D B Property Enterprises Limited | Construction | 2024 |
| D Clarke Management Ltd | Financial services | 2018 |
| D G Carvell Groundworks Ltd | Construction | 2012 |
| D G Morris (Properties) Ltd | Hospitality | 2004 |
| D Gray Transport Limited | Transport & logistics | 2017 |
| D J 05 Investments Ltd | Real estate | 2024 |
| D J Autos (Swansea) Limited | Wholesale & retail | 2009 |
| D J Morgan Roofing Ltd | Construction | 2024 |
| D J Pickard Limited | Financial services | 2013 |
| D J Romano & SON Limited | Construction | 2007 |
| D J Williams & SON Limited | Construction | 2014 |
| D Jackson Removals Ltd | Transport & logistics | 2014 |
| D John Ltd | Professional & scientific | 2026 |
| D Jones Tape & Jointing Ltd | Extraterritorial | 2024 |
| D L Couriers Limited | Transport & logistics | 2024 |
| D M Morgan & Co. Limited | Professional & scientific | 2002 |
| D N a Wealth Limited | Financial services | 2006 |
| D P Architecture Ltd | Administrative & support | 2007 |
| D P Forwarding (South Wales) Limited | Other services | 1996 |
| D R M (Steel Supplies) Limited | | 1982 |
| D Richards Fitness Ltd | Arts & recreation | 2019 |
| D Richards Limited | Other services | 2015 |
| D Rossiter Construction Ltd | Construction | 2015 |
| D S Executive Travel Services Limited | Transport & logistics | 2022 |
| D Saunders Roofing and Building Ltd | Construction | 2022 |
| D T Drilling Maintenance Ltd | Manufacturing | 2024 |
| D&A Service Repair &MOT Ltd | Wholesale & retail | 2025 |
| D&B Cars Ltd | Wholesale & retail | 2020 |
| D&P Management Services Limited | Professional & scientific | 2025 |
| D&S Flat Roofing Ltd | Construction | 2024 |
| D&T Developments Ltd | Real estate | 2020 |
| D'Marble Limited | Wholesale & retail | 2025 |
| D. Bamber Surveys Limited | Construction | 1999 |
| D. R. Richards Limited | Wholesale & retail | 1975 |
| D.B.C. Site Services 2005 Ltd | Wholesale & retail | 2005 |
| D.D.Evans & Co.,Limited | Wholesale & retail | 1940 |
| D.F.& A.M.Bevan & Co.,Limited | Wholesale & retail | 1961 |
| D.G. Moses Plant Hire Limited | Construction | 1997 |
| D.G.S Tyre and Garage Services Ltd | Wholesale & retail | 2020 |
| D.H.A. (Wales) Limited | Construction | 1996 |
| D.H.Strawbridge Limited | Wholesale & retail | 1941 |
| D.L. & H. Griffiths & Sons Limited | Agriculture & fishing | 1984 |
| D.M.T Gould Limited | Professional & scientific | 2001 |
| D.R.C. Developments Limited | Real estate | 2025 |
| D.S.A Properties Swansea Ltd | Real estate | 2026 |
| D5L Ltd | Information & communication | 2021 |
| Da-Sh Property Ltd | Construction | 2025 |
| Dabek Building Services Ltd | Construction | 2024 |
| DAC Machine Repairs Ltd | Manufacturing | 2022 |
| Daddi Israel Transportation. Limited | Wholesale & retail | 2025 |
| Daffodil Artificial Intelligence Ltd | Information & communication | 2025 |
| Daffodil Innovations Limited | Extraterritorial | 2025 |
| DAG Construction Limited | Construction | 2010 |
| Dagnut Limited | Construction | 2018 |
| Dahuama Limited | Health & social care | 2023 |
| DAI Dugitt Limited | Administrative & support | 2024 |