| Hwyl a Fflag CYF | Administrative & support | 2006 |
| IAR Capital Ltd | Health & social care | 2024 |
| IG Education (Cardiff) Limited | Education | 2026 |
| Ilyas Marketing Ltd | Administrative & support | 2026 |
| Inboxstyle Ltd | Professional & scientific | 2025 |
| Indian Fairwater Tandoori Ltd | Hospitality | 2026 |
| Indie Property Ltd | Real estate | 2025 |
| Innovaitive Solutions Ltd | Professional & scientific | 2025 |
| International Limited | Extraterritorial | 2015 |
| IO Takeaway Ltd | Hospitality | 2024 |
| Isgar Associates Ltd | Health & social care | 2025 |
| Ishtiaq & Sons Ltd | Transport & logistics | 2026 |
| Itgel Ltd | Construction | 2026 |
| J & J Worldwide Ltd | Wholesale & retail | 2024 |
| Jafar Iqbal Productions Ltd | Arts & recreation | 2025 |
| Jandkwholesale Ltd | Wholesale & retail | 2024 |
| JC3HUB Ltd | Wholesale & retail | 2025 |
| Jdistribution Ltd | Wholesale & retail | 2026 |
| Jethro Care Ltd | Health & social care | 2026 |
| JHA Retail Group Ltd | Professional & scientific | 2024 |
| Jhdtrading Ltd | Wholesale & retail | 2025 |
| JJ Apex Exteriors Ltd | Professional & scientific | 2026 |
| JOE Tannorella Ltd | Professional & scientific | 2024 |
| Johanna Brooks Property Group Ltd | Real estate | 2025 |
| Johnson Continental Ltd | Real estate | 2023 |
| Jowithlove Ltd | Wholesale & retail | 2026 |
| JVM Clinical Support Ltd | Health & social care | 2026 |
| Kapra Web Ltd | Wholesale & retail | 2024 |
| Kaya Electrical Cardiff Ltd | Hospitality | 2025 |
| KDB Properties Ltd | Real estate | 2024 |
| Khalifa Limited | Transport & logistics | 2026 |
| Kingdomworks Ltd | Wholesale & retail | 2026 |
| Kiswah Collection Ltd | Professional & scientific | 2026 |
| Knights Chess Academy Ltd | Education | 2026 |
| KO Accounting Ltd | Professional & scientific | 2025 |
| L P Murphy Ltd | Administrative & support | 2026 |
| Laaalish Ltd | Wholesale & retail | 2025 |
| Landforte Partners Ltd | Real estate | 2026 |
| Lansdown Painting Co. Ltd | Construction | 2026 |
| Laundrette Cardiff Ltd | Administrative & support | 2026 |
| LEW Construction Management Ltd | Construction | 2025 |
| Libamed Ltd | Information & communication | 2026 |
| Light Waste and Building Services Ltd | Water & waste | 2026 |
| Lindor Shop Ltd | Wholesale & retail | 2026 |
| LKB Holdings Ltd | Financial services | 2025 |
| LNZ Digital Ltd | Professional & scientific | 2025 |
| Load-Safe Logistics Ltd | Transport & logistics | 2026 |
| Loney Engineering Limited | Professional & scientific | 2026 |
| Lovehere Ltd | Hospitality | 2025 |
| Lovehere Properties Ltd | Real estate | 2026 |
| Lovetomove Ltd | Wholesale & retail | 2025 |
| Lowri Angharad Ltd | Health & social care | 2025 |
| LS Housing Properties Ltd | Real estate | 2026 |
| Luke Oliver Grips Ltd | Information & communication | 2026 |
| Lumerowellness Ltd | Wholesale & retail | 2026 |
| Lush Living Cleaning Co. Ltd | Administrative & support | 2025 |
| Luxuryballonsbymay Events Ltd | Hospitality | 2025 |
| M&B Accommodations Ltd | Real estate | 2025 |
| M&G Collective Ltd | Professional & scientific | 2026 |
| Main Land Stone Ltd | Administrative & support | 2022 |
| MAK Trading London Ltd | Wholesale & retail | 2024 |
| Make Your Will Today Limited | Professional & scientific | 2008 |
| Malone's Services Ltd | Wholesale & retail | 2025 |
| Manning Memorabilia Ltd | Wholesale & retail | 2025 |
| Mansel Law Consultancy Ltd | Professional & scientific | 2025 |
| Mary Jane Dispensary Ltd | Wholesale & retail | 2025 |
| Marysa ZEA Ltd | Professional & scientific | 2024 |
| Master Material Trading Ltd | Wholesale & retail | 2026 |
| Maudizon Limited | Health & social care | 2022 |
| Melanite Jewels Ltd | Wholesale & retail | 2026 |
| Menter Caerdydd | Education | 2002 |
| Metacore Logistics Ltd | Transport & logistics | 2025 |
| Miandson Holdings Ltd | Wholesale & retail | 2024 |
| Microbiton Ltd | Information & communication | 2024 |
| Minimal Bar Ltd | Hospitality | 2023 |
| MMY Reality Ltd | Manufacturing | 2026 |
| Mobile Detailing Valet Service Ltd | Administrative & support | 2024 |
| Moethus Limited | Extraterritorial | 2014 |
| Mohammed K Ltd | Transport & logistics | 2026 |
| MOO Alhaji Ltd | Transport & logistics | 2026 |
| Morgan and Rowlands Ltd | Real estate | 2024 |
| Mosey Ltd | Information & communication | 2026 |
| Move ANY Where Ltd | Transport & logistics | 2026 |
| MR Bashar Ltd | Transport & logistics | 2026 |
| MR GAS Heating and Plumbing Ltd | Construction | 2025 |
| Mrbodyshop UK Ltd | Wholesale & retail | 2024 |
| Mubarak Qorane Ltd | Transport & logistics | 2026 |
| Muffet Vintage Ltd | Wholesale & retail | 2026 |
| Myaa Events Co. Ltd | Professional & scientific | 2025 |
| Mysushicardiff Ltd | Manufacturing | 2026 |
| N&R SON Limited | Hospitality | 2020 |
| NA NA Productions Holdings Limited | Information & communication | 2016 |
| NAC Building Ltd | Construction | 2026 |
| Nails by Ella Ltd | Other services | 2025 |
| Nata&Co Bakery Ltd | Hospitality | 2025 |
| National Aquatic Training Centre Ltd | Arts & recreation | 2026 |
| Neon Sushi Ltd | Professional & scientific | 2025 |
| Newton’ Kitchen Ltd | Hospitality | 2026 |
| Nicholas Building & Renovations Ltd | Construction | 2026 |
| Nile Logistics Ltd | Transport & logistics | 2026 |