| Hillton Carpentry Services Limited | Construction | 2016 |
| Hintbest Limited | Construction | 1985 |
| Histopathology Limited | Health & social care | 2010 |
| Hive on the Quay Limited (the) | Real estate | 1975 |
| HJB Davies (Roofing) Limited | Construction | 2005 |
| HLJ27 Ltd | Agriculture & fishing | 2016 |
| Holly Kingsbury Limited | Manufacturing | 2023 |
| Holmes Contracting Ltd | Water & waste | 2014 |
| Housa Pathology Services Limited | Health & social care | 2023 |
| Houseboats and Barges Limited | Construction | 2015 |
| Howells Eyecare & Consulting Ltd | Financial services | 2024 |
| Howgillsculinary Ltd | Hospitality | 2021 |
| Howgillshospitality Ltd | Hospitality | 2021 |
| Howies Limited | Wholesale & retail | 1995 |
| HPS Investments Ltd | Real estate | 2025 |
| HR James Construction Ltd | Construction | 2016 |
| Hufen IA Upton Ltd | Wholesale & retail | 2025 |
| Huggi Homes Ltd | Real estate | 2024 |
| Hughes Blaendyffryn Limited | Agriculture & fishing | 2003 |
| Hughes Fresh Fruit Ltd | Wholesale & retail | 2003 |
| Hughes Tree and Garden Services Limited | Administrative & support | 2022 |
| Hugo & Aria Services Ltd | Manufacturing | 2025 |
| Hummingbird Publishing Ltd | Information & communication | 2024 |
| Hvaow Ltd | Information & communication | 2020 |
| Hygeia Cardiac Diagnosis Limited | Health & social care | 2021 |
| I Build (Wales) Limited | Construction | 2006 |
| I Design (Wales) Limited | Manufacturing | 2014 |
| I K Prem Ltd | Wholesale & retail | 2025 |
| I L J Limited | Other services | 2025 |
| I&Dc Limited | Professional & scientific | 2000 |
| I.J. Morgan Heating & Renewables Ltd | Construction | 2019 |
| Iago Cymru CYF | Professional & scientific | 2002 |
| IAN Thomas Construction Services Limited | Construction | 1990 |
| Iconic Property Solutions Limited | Real estate | 2026 |
| Ideation Technology Ltd | Information & communication | 2016 |
| IDP Maintenance Ltd | Construction | 2018 |
| IDP Solutions (Midlands) Limited | Construction | 2016 |
| Imagine Recruitment Ltd | Real estate | 2014 |
| Imal Properties (Swansea) Ltd | Real estate | 2025 |
| Imergence Ltd | Construction | 2005 |
| Immortal House Limited | Professional & scientific | 2017 |
| Imperial Laser Whitening Ltd | Wholesale & retail | 2022 |
| Impexcom PC | | 2018 |
| Improved YOU Ltd | Administrative & support | 2016 |
| Imstokze Ltd | Professional & scientific | 2026 |
| In-House Properties Ltd | Extraterritorial | 2000 |
| Independent Thinking Limited | Education | 1994 |
| Indian Imports Ltd | Wholesale & retail | 2022 |
| Individual Psychology Training CIC | Education | 2022 |
| Inferno Design and Consultancy Limited | Construction | 2024 |
| Infinity Bar Carmarthen Ltd | Hospitality | 2022 |
| Informatic Integration Limited | Information & communication | 2013 |
| Informesen Limited | Information & communication | 2017 |
| Ingram Tribology Ltd | Professional & scientific | 2018 |
| Inn at the Sticks Limited | Hospitality | 2023 |
| Innisfree Complex Ltd | Real estate | 2006 |
| Insignia Technology Systems Limited | Information & communication | 2010 |
| Intercadfan Limited | Professional & scientific | 2012 |
| Interiv Engineering Ltd | Professional & scientific | 2026 |
| International Consultancy and Resource Enterprise | Health & social care | 1999 |
| International Wildlife Consultants (UK) Limited | Agriculture & fishing | 2006 |
| Internetworking Ltd | Information & communication | 2022 |
| Interproxchange Ltd | Professional & scientific | 2020 |
| Intragas (Cardiff) Ltd | Construction | 2020 |
| Intrasign Ltd | Manufacturing | 2024 |
| Invicta Care Homes Limited | Health & social care | 2007 |
| IQ Learning Group Ltd | Information & communication | 2023 |
| Isabelle Trading Limited | Professional & scientific | 2025 |
| Isabelleco Limited | Professional & scientific | 2023 |
| Isbj (Consultants) Limited | Professional & scientific | 1998 |
| Isbj (Properties) Limited | Other services | 1998 |
| Iscoed Geoconsulting Ltd | Professional & scientific | 2016 |
| Island House Restoration Ltd | Construction | 2020 |
| Ivision Ltd | Health & social care | 2022 |
| IVY Bush Limited | Hospitality | 2026 |
| J & F Motors Ltd | Wholesale & retail | 2026 |
| J & L Morgan Limited | Real estate | 2024 |
| J & S Capital Investment Ltd | Real estate | 2022 |
| J a G Hicks Minibus Hire Limited | Transport & logistics | 2023 |
| J B Ashwell Limited | Manufacturing | 2026 |
| J B Carpentry & Joinery Services Limited | Construction | 2026 |
| J D Williams Inspection Limited | Professional & scientific | 2016 |
| J J Aggregates Limited | Transport & logistics | 2004 |
| J L G Recovery Limited | Wholesale & retail | 2025 |
| J Load Inc Limited | Arts & recreation | 2019 |
| J M Duxberry Plumbing and Heating Ltd | Construction | 2003 |
| J M G Fabrication Services Limited | Manufacturing | 2026 |
| J N Williams Ground Maintenance Limited | Administrative & support | 2001 |
| J P Webb Properties Limited | Real estate | 2017 |
| J Priestley Therapy Practice Limited | Health & social care | 2003 |
| J&J Property Group Limited | Real estate | 2020 |
| J.B. Building & Renovation Ltd | Construction | 2026 |
| J.C. Joinery & Cabinet Makers Ltd | Construction | 2015 |
| J.D. & M. Morgan Limited | Agriculture & fishing | 1984 |
| JAB Inc Ltd | Other services | 2022 |
| Jack Parker Plumbing and Heating Ltd | Construction | 2019 |
| Jackie James Ltd | Wholesale & retail | 2010 |
| Jacomm Systems Limited | Extraterritorial | 1996 |
| JAG Ecoenergy Ltd | Energy | 2014 |
| JAH Property Development Limited | Construction | 2016 |