| KMB Restaurant Ltd | Hospitality | 2025 |
| Knock Knock Cricket Ltd | Wholesale & retail | 2016 |
| KR Cables Ltd | Construction | 2025 |
| Kristian Thomas Painting & Decorating Specialist Ltd | Construction | 2025 |
| KSJ (RCT) Limited | Other services | 2016 |
| KTV Working Drone (UK) Ltd | Professional & scientific | 2022 |
| Kudos Hair Advice Centre Limited | Other services | 2005 |
| L Smith & SON Roofing Ltd | Construction | 2024 |
| L&L Bodyworx Ltd | Wholesale & retail | 2023 |
| LA Lloma Limited | Real estate | 1969 |
| LA Prospectif Limited | Professional & scientific | 2025 |
| LA Taqueria Limited | Hospitality | 2025 |
| Laboris Law Ltd | Professional & scientific | 2021 |
| Lake House Retreat Ltd | Hospitality | 2025 |
| Landev Consult Limited | Professional & scientific | 2022 |
| Lanelay Hall Limited | Hospitality | 2017 |
| Lanternroofblinds Limited | Manufacturing | 2021 |
| Lara Rose Training Academy Ltd | Education | 2025 |
| Lass Enterprises Limited | Real estate | 2013 |
| LB Electrical & Property Maintenance Limited | Construction | 2024 |
| Lchem GAS Supplies Ltd | Energy | 2026 |
| Learned Consulting Limited | Education | 2026 |
| Leekes Limited | Wholesale & retail | 1956 |
| Legacy Pilates Ltd | Arts & recreation | 2025 |
| Leigh Christopher Haulage Limited | Transport & logistics | 2017 |
| LEO Property Investment Group Limited | Real estate | 2021 |
| Leopard Lettings Limited | Real estate | 2019 |
| Lewis Capital Limited | Administrative & support | 2010 |
| Leyshons Fish Bar Limited | Hospitality | 2002 |
| Lifestyle (Glamorgan) Limited | Financial services | 2006 |
| Lifting Gear Services Limited | Manufacturing | 2018 |
| Light Therapy Lounge Ltd | Other services | 2024 |
| Lighting UP Events UK Ltd | Administrative & support | 2022 |
| Limestone Events & Exhibitions Ltd | Administrative & support | 2024 |
| Linelevel Ltd | Construction | 2025 |
| Little Acorns 50 Limited | Wholesale & retail | 2017 |
| Little Haven Nurseries Ltd | Education | 2021 |
| Little Inspirations Limited | Health & social care | 2003 |
| Little Loves Photography Ltd | Professional & scientific | 2025 |
| Littlebluestarcrafts Limited | Manufacturing | 2025 |
| Live Captioning UK Ltd | Administrative & support | 2015 |
| Live Vida Ltd | Manufacturing | 2019 |
| LJS Wholesale Ltd | Other services | 2014 |
| Ljsr Limited | Manufacturing | 2022 |
| Ljsr Property Limited | Construction | 2024 |
| LK Carpets Limited | Other services | 2017 |
| LK Estates Management Limited | Other services | 2017 |
| Llanharan Community Development Project Ltd | Health & social care | 1996 |
| Llanharan Pharmacy Limited | Wholesale & retail | 2000 |
| Llantrisant Developments Limited | Construction | 2004 |
| Llantrisant Electrical Services and Sales Limited | Construction | 1995 |
| Llantrisant Recycling Centre Limited | Water & waste | 2015 |
| Llantrisant Tennis Club Limited | Arts & recreation | 2021 |
| LMB Auto Products Ltd | Wholesale & retail | 2025 |
| LML Electrical Limited | Construction | 2022 |
| Lockett Boxing and Fitness Limited | Arts & recreation | 2013 |
| Lodestone Professional Solutions Ltd | Professional & scientific | 2005 |
| Loganjamesco Ltd | Wholesale & retail | 2025 |
| Lomax Facility Solutions Limited | Construction | 2024 |
| Loving Welsh Food CYF | Administrative & support | 2025 |
| Lucia EVA Beauty Ltd | Other services | 2025 |
| Lumi Event Design Limited | Administrative & support | 2016 |
| Lunar Eclipse Properties Ltd | Real estate | 2023 |
| Lutra Consultancy Ltd | Professional & scientific | 2023 |
| Luxury Event Decor Wales Ltd | Professional & scientific | 2023 |
| Lyons DEN Property Investment Limited | Real estate | 2017 |
| Lyons DEN Security Limited | Administrative & support | 2022 |
| M Hope Capital Ltd | Real estate | 2019 |
| M J Design Architectural Services Ltd | Professional & scientific | 2020 |
| M&M Commercial Repairs Limited | Wholesale & retail | 2004 |
| M.J.E Goods and Services Ltd | Wholesale & retail | 2019 |
| M.W. Promotions Limited | Financial services | 2005 |
| Mackintosh Estates Ltd. | Real estate | 2017 |
| Maclean Realtime Text Ltd | Professional & scientific | 2018 |
| Maisie Bolan Associates Ltd | Professional & scientific | 2018 |
| Maison Anwen Limited | Wholesale & retail | 2025 |
| Malk Residential Ltd | Real estate | 2020 |
| Manbha Limited | Health & social care | 2021 |
| Maranathagrace Limited | Health & social care | 2023 |
| Marchio Holdings Ltd | Financial services | 2022 |
| Marcus Emporium Limited | Wholesale & retail | 2013 |
| Marie's Journey Ltd | Administrative & support | 2020 |
| Marić Asset Management Limited | Real estate | 2024 |
| Marić Group Limited | Financial services | 2026 |
| Marić Properties Limited | Real estate | 2026 |
| Mark Stephen Laing Limited | Extraterritorial | 2025 |
| Marlis Bookkeeping & Accountancy Limited | Professional & scientific | 2022 |
| Marmalade TV Ltd | Information & communication | 2019 |
| Martha Reed Ltd | Information & communication | 2024 |
| Masterclass Tennis Ltd | Arts & recreation | 2011 |
| Matthew Newland Ltd | Health & social care | 2008 |
| Mbmr Limited | Wholesale & retail | 2024 |
| Mcandrew Travel Ltd | Administrative & support | 2023 |
| Mccolgan Astrum Investments Ltd | Financial services | 2023 |
| Mccolgan Astrum Space Limited | Information & communication | 2022 |
| Medical Intelligence Systems Ltd | Wholesale & retail | 2023 |
| Medusa Construction Cosmetics Limited | Construction | 2012 |
| Melinfa Holdings Ltd | Real estate | 2022 |
| Melinfa Properties Ltd | Construction | 2017 |
| Melodyit Limited | Education | 2014 |