| JD Cafe Ltd | Hospitality | 2025 |
| JD Collette Ltd | Transport & logistics | 2025 |
| JD Homes Newport Ltd | Real estate | 2023 |
| JD Stores Ltd | Wholesale & retail | 2020 |
| JDY Electrical Services Ltd | Construction | 2021 |
| Jecca Blac Limited | Other services | 2017 |
| Jena Retail Ltd | Wholesale & retail | 2021 |
| Jenic Plant Services Limited | Construction | 2016 |
| Jera Creative Agency Limited | Administrative & support | 2018 |
| Jeremy Yeates Limited | Manufacturing | 2000 |
| Jerun Jesmi Ltd | Wholesale & retail | 2025 |
| Jewell Financial Limited | Financial services | 2007 |
| Jggt Pizza Ltd | Hospitality | 2023 |
| Jgtinvestments Ltd | Professional & scientific | 2023 |
| JJ Landscaping and Gardening Ltd | Administrative & support | 2025 |
| Jjmzkd Ltd | Professional & scientific | 2025 |
| JLA Roofing CYF | Construction | 2025 |
| JLL HUT (UK) Limited | Financial services | 2022 |
| JMA Cwmbran Ltd | Hospitality | 2024 |
| JN HR Limited | Professional & scientific | 2018 |
| JOB Done Renovations Ltd | Construction | 2026 |
| Jordan Jewellery Design Limited | Wholesale & retail | 2006 |
| Joyce Estates Limited | Real estate | 2023 |
| Jppw Poultry Limited | Administrative & support | 2007 |
| Jpubs Ltd | Hospitality | 2022 |
| JR Holdings Group Ltd | Manufacturing | 2019 |
| JR Home Estates Limited | Real estate | 2025 |
| Jsjp Properties Limited | Real estate | 2019 |
| JT Parties Ltd | Arts & recreation | 2026 |
| JT87 Limited | Real estate | 2023 |
| Julian Mark Limited | Other services | 2013 |
| Just Air Fabrications Ltd | Manufacturing | 2020 |
| Just for Property Ltd | Real estate | 2008 |
| Just-Build UK. Ltd | Construction | 2019 |
| K & M Energy Surveys Ltd | Professional & scientific | 2023 |
| K B Building Contractors Limited | Construction | 2017 |
| K E and L R C Edwards Limited | Agriculture & fishing | 2008 |
| K J a G Holdings Limited | Real estate | 2025 |
| K J a G Properties Ltd | Real estate | 2022 |
| K J Building Developers Ltd | Construction | 2025 |
| K&J Ventilation Ltd | Professional & scientific | 2025 |
| K.V. Rollers Limited | Manufacturing | 1988 |
| Kalnas Group Ltd | Information & communication | 2020 |
| Kalon Clinic Ltd | Other services | 2025 |
| Kalow Ltd | Financial services | 2022 |
| Karvor Properties Limited | Real estate | 2023 |
| Kashiko Limited | Information & communication | 2013 |
| Kashman Wealth Limited | Professional & scientific | 2025 |
| Kaspa's Cwmbran Ltd | Hospitality | 2016 |
| KAT Gardening Services CYF | Other services | 2025 |
| Kavod Property Ltd | Real estate | 2022 |
| Kavod Roofing & Construction Ltd | Construction | 2025 |
| KDF Property Limited | Real estate | 2023 |
| KDK Metals Limited | Wholesale & retail | 2007 |
| Keane Motorz Ltd | Wholesale & retail | 2025 |
| Kelly's Houseplant HUT Ltd | Wholesale & retail | 2025 |
| Kepria Limited | Professional & scientific | 2024 |
| Ketchlove Properties Ltd | Real estate | 2025 |
| Key Development Solution Limited | Professional & scientific | 2013 |
| Keyport Land Limited | Agriculture & fishing | 1976 |
| Khaime Ltd | Professional & scientific | 2026 |
| Kicher Ltd | Other services | 2025 |
| Kickstart Scooters Ltd | Wholesale & retail | 2025 |
| Kilted Dragon Distillery Ltd | Manufacturing | 2025 |
| KIM Kitchen Limited | Hospitality | 2025 |
| Kinetic Development Solutions Limited | Administrative & support | 2025 |
| Kinetic Workplace Limited | Administrative & support | 2007 |
| KJ Property South Wales Ltd | Real estate | 2024 |
| Kjar Aesthetics Limited | Education | 2022 |
| Kkcwmbran Ltd | Hospitality | 2025 |
| KL Technical Services Limited | Professional & scientific | 2025 |
| KLS Hair & Beauty Ltd | Other services | 2020 |
| Km&K Limited | Real estate | 2017 |
| Kmdsd Limited | Real estate | 2016 |
| Kndl Property Ltd | Real estate | 2026 |
| Koma Creations Limited | Manufacturing | 2025 |
| KOS DEG Ltd | Hospitality | 2025 |
| KST Property and Letting Ltd | Real estate | 2026 |
| Kylo's Grill Ltd | Hospitality | 2023 |
| L & J Engineering Limited | Manufacturing | 2002 |
| L Golledge Roofing Limited | Construction | 2023 |
| L W Engineering Ltd | Manufacturing | 2008 |
| L&L Scaffolding Solutions Ltd | Construction | 2025 |
| L.D.Building Ltd | Construction | 2022 |
| LA Rossina Ltd | Hospitality | 2020 |
| Lacutz Limited | Other services | 2022 |
| Lafaat Limited | Information & communication | 2023 |
| Landlady Laura Ltd | Real estate | 2026 |
| Landrover Specialist Autos Ltd | Wholesale & retail | 2025 |
| Laporsa Ltd | Wholesale & retail | 2013 |
| Laporsa Properties Limited | Real estate | 2016 |
| LAR Newport Limited | Administrative & support | 2018 |
| Largercoast Group Ltd | Construction | 2022 |
| Lawrence Miller & Co Limited | Financial services | 2010 |
| Lawrence Miller Properties Limited | Real estate | 2009 |
| LE Used Car Sales Limited | Wholesale & retail | 2024 |
| Learnalytics Limited | Education | 2022 |
| LED Sealants Ltd | Construction | 2024 |
| LEE Saunders Engineering Limited | Manufacturing | 2016 |
| Leetech GAS Engineers Ltd | Construction | 2009 |