| John Marshall and Company(Cardiff and Barry),Limited | Wholesale & retail | 1911 |
| Jolo Clan Limited | Professional & scientific | 2022 |
| Jonathan Stauber Solar Consultant Ltd | Wholesale & retail | 2024 |
| Jones QA Ltd | Professional & scientific | 2025 |
| Jose Holt Ltd | Financial services | 2023 |
| JP Design & Construction Management Limited | Professional & scientific | 2002 |
| JPN Accountancy Services Limited | Professional & scientific | 2012 |
| JQ Catering Services Ltd | Hospitality | 2016 |
| JRC Bits ‘N’ Bobs Ltd | Transport & logistics | 2025 |
| JS Construction (ST Athan) Limited | Construction | 2020 |
| JSH Plumbing & Heating Ltd | Construction | 2017 |
| JSI Engineering Consultancy Ltd | Professional & scientific | 2019 |
| JSI Investment Property Ltd | Real estate | 2025 |
| JSM Garden Services Ltd | Administrative & support | 2012 |
| Jt.Bs South Wales Ltd | Construction | 2026 |
| Jules Property Agent Ltd | Real estate | 2020 |
| Julie's Plaice Barry Ltd | Hospitality | 2026 |
| Juno T&S Consultancy Ltd | Manufacturing | 2021 |
| JV Trees Ltd | Agriculture & fishing | 2022 |
| Jwcr Limited | Professional & scientific | 2019 |
| JWP Financial Ltd | Financial services | 2025 |
| K Enfield Stays Limited | Real estate | 2025 |
| K&K Fast Food Ltd | Hospitality | 2022 |
| K-Start Railmedia Ltd | Construction | 2025 |
| K.C.S. Transport Limited | Transport & logistics | 1994 |
| Kaleidatone Worldwide Ltd | Construction | 2018 |
| Kalimirch Barry Limited | Hospitality | 2022 |
| Karen's Occasions Ltd | Hospitality | 2024 |
| Karim Car Products Ltd | Wholesale & retail | 2023 |
| Karmarts Lucky Limited | Wholesale & retail | 2025 |
| Karo Travel Limited | Transport & logistics | 2020 |
| Karsen Ltd | Wholesale & retail | 2025 |
| Kartz Ltd | Hospitality | 2025 |
| Katie Cecil Aesthetics Limited | Health & social care | 2019 |
| KCW Property Ltd | Real estate | 2025 |
| KE Tamplin Limited | Professional & scientific | 2024 |
| Keita Enfield Properties Limited | Real estate | 2022 |
| Kells Properties Ltd | Construction | 2025 |
| Kelly Holdings Limited | Financial services | 2025 |
| Kennedy Ames Ltd | Professional & scientific | 2019 |
| Kenny Property Investments Ltd | Real estate | 2025 |
| Kenny`S Park Limited | Real estate | 2007 |
| Kerala Food Beats Ltd | Hospitality | 2025 |
| Keshra & Gopal Ltd | Wholesale & retail | 2023 |
| Kevin Myles Ltd | Arts & recreation | 2025 |
| Khalid Ghani Family Education Foundation Limited | Education | 2025 |
| Kiet Nails Ltd | Other services | 2025 |
| Kinging-It Ltd | Arts & recreation | 2016 |
| Kirrin Homes Limited | Construction | 1999 |
| Kitchen Spraying Wales Ltd | Construction | 2021 |
| Kitchens for Living (Barry) Ltd | Manufacturing | 2017 |
| Kitley Interpreting and Translation Services Ltd | Professional & scientific | 2026 |
| Kits-N-Bits Limited | Wholesale & retail | 2003 |
| Kiyara Ltd | Wholesale & retail | 2022 |
| KM Industrial Maintenance Ltd | Manufacturing | 2026 |
| KN Real Estate Management Ltd | Real estate | 2021 |
| KOB Limited | Real estate | 2024 |
| Koya Construction Limited | Professional & scientific | 2025 |
| Koya Group Limited | Real estate | 2026 |
| Koya Lettings Limited | Real estate | 2025 |
| Koya Properties Limited | Construction | 2019 |
| KPR Building & Roofing Limited | Construction | 2025 |
| Kraken Supplies Ltd | Wholesale & retail | 2013 |
| Kribelle Property Investments Ltd | Real estate | 2025 |
| Kruger & Co Limited | Administrative & support | 2013 |
| KTC Maintenance Ltd | Construction | 2015 |
| Kumar's Island Ltd | Hospitality | 2025 |
| KVL Retail Ltd | Wholesale & retail | 2020 |
| Kynaston Property Ltd | Real estate | 2025 |
| L & P Property Letting Limited | Real estate | 2016 |
| L a Industrial Supplies Limited | Wholesale & retail | 2007 |
| L C G Engineering Services Limited | Manufacturing | 2016 |
| L J Air Conditioning Ltd | Construction | 2018 |
| L N C Floor Coverings Ltd | Wholesale & retail | 2005 |
| L V Building Services Limited | Construction | 2016 |
| L&A Engineering Ltd | Professional & scientific | 2025 |
| L&O Scaffolding Services Limited | Construction | 2025 |
| L. a. Bridgeman Ductwork Ltd | Construction | 2018 |
| L.M.N Property Maintenance Ltd | Construction | 2014 |
| L.S Logistics Ltd | Administrative & support | 2025 |
| LA Petite Fromagerie Limited | Hospitality | 2019 |
| LA Pinoz Pizza Ltd | Hospitality | 2025 |
| LA Refurbishments Limited | Construction | 2025 |
| Ladders UK Direct Ltd | Wholesale & retail | 2012 |
| Lailna & Sons Investments Limited | Real estate | 2019 |
| Lailna Stores Limited | Wholesale & retail | 2014 |
| Lakin Accountancy Services Limited | Professional & scientific | 2004 |
| Lalita Luxe Limited | Wholesale & retail | 2025 |
| Lams 235 Limited | Hospitality | 2021 |
| Lapsing Limited | Information & communication | 2022 |
| Laser Llama Designs Ltd | Wholesale & retail | 2018 |
| Lawn Nation Concepts Ltd | Wholesale & retail | 2014 |
| LB Osteopathy Ltd | Health & social care | 2026 |
| LC Management Solutions Ltd | Construction | 2024 |
| LCB Solutions Ltd | Other services | 2021 |
| LCG Lettings Ltd | Real estate | 2026 |
| LCL Holdings Ltd | Real estate | 2021 |
| Lcva Services Ltd | Administrative & support | 2019 |
| LD Property Co Investments Ltd | Real estate | 2023 |
| LE & LE Management Limited | Real estate | 2026 |