| Killay Ground Rents Limited | Real estate | 2021 |
| Killay Health & Fitness Club Ltd | Health & social care | 2017 |
| Killay Lettings Limited | Real estate | 2014 |
| Killay Properties Limited | Construction | 1985 |
| Kilomet Limited | Real estate | 2021 |
| Kilvey Capital Holdings Limited | Real estate | 2024 |
| Kilvey Ltd | Wholesale & retail | 2026 |
| Kilvey Mini Travel / Kilvey Cabs Ltd | Transport & logistics | 2007 |
| Kimdale Matrix Limited | Professional & scientific | 2001 |
| KIN Protect Ltd | Financial services | 2025 |
| Kindcocoa Ltd | Wholesale & retail | 2022 |
| Kinder Restaurants Limited | Hospitality | 2016 |
| King & Morse Limited | Real estate | 2010 |
| King of Spades Ltd | Information & communication | 2019 |
| Kingfisher Centre Ltd | Wholesale & retail | 2024 |
| Kingman Developments Limited | Real estate | 2022 |
| Kings Court (Wales) Limited | Real estate | 2011 |
| Kingsbridge Print Limited | Manufacturing | 2002 |
| Kingsbridge Storage Ltd | Transport & logistics | 2026 |
| Kingsden Digital Agency Ltd | Information & communication | 2021 |
| Kingship Fowey Limited | Hospitality | 2022 |
| Kingston Accommodation Services Ltd | Hospitality | 2023 |
| Kington Roofing Services Limited | Construction | 2008 |
| Kinship House Limited | Professional & scientific | 2015 |
| KIP Mcgrath Tuition Swansea LP | | 2015 |
| Kiranmayi Battula Ltd | Information & communication | 2022 |
| Kirstie Logan Communications Limited | Professional & scientific | 2026 |
| Kirsty's Home&Help Services Ltd | Administrative & support | 2025 |
| Kirstys Beauty Suite Ltd | Other services | 2018 |
| Kiss & Make UP Beauty & Aesthetics Ltd | Other services | 2026 |
| KIT SB Limited | Administrative & support | 2021 |
| Kitchens by Emma Reed Limited | Wholesale & retail | 2018 |
| Kite Valley Kitchens Ltd | Manufacturing | 2026 |
| Kittle Country Stores Limited | Wholesale & retail | 2021 |
| Kittle Village Bakery Limited | Hospitality | 2004 |
| KJ Builds Ltd | Construction | 2025 |
| KJ Media Ltd | Information & communication | 2020 |
| Kjdw Limited | Administrative & support | 2015 |
| Kjdw Property Limited | Real estate | 2017 |
| Kjme Limited | Administrative & support | 2017 |
| Kjnh Retail Group Limited | Wholesale & retail | 2025 |
| KJR Limited | Information & communication | 2000 |
| KJS Real Estate Limited | Real estate | 2025 |
| KK Trading Group Ltd | Wholesale & retail | 2023 |
| KL Garden & Property Services Ltd | Administrative & support | 2026 |
| KL Property Group Ltd | Real estate | 2025 |
| Klad DU Mond Ltd | Arts & recreation | 2020 |
| Klaia Ltd | Wholesale & retail | 2024 |
| Klasse Group Ltd | Construction | 2017 |
| Klaymio Ltd | Financial services | 2023 |
| Klem&B Property Management&Maintenance Ltd | Real estate | 2024 |
| KLJ Babaji Ltd | Hospitality | 2020 |
| KLJ Babaji Properties Ltd | Real estate | 2023 |
| KLM Traders Ltd | Wholesale & retail | 2024 |
| Kloodos Wellness Ltd | Manufacturing | 2018 |
| Kluski Properties Limited | Real estate | 2024 |
| KLV Villas Ltd | Hospitality | 2022 |
| KLW Consultancy Limited | Health & social care | 2023 |
| KLY CAD Limited | Professional & scientific | 2017 |
| KLY Invest Ltd | Real estate | 2024 |
| KMA Accountants Limited | Professional & scientific | 1986 |
| Kmci Services Ltd | Manufacturing | 2017 |
| KMG Holdings Ltd | Water & waste | 2018 |
| Kneath Associates Ltd | Information & communication | 1998 |
| Kngs Seafood Ltd | Wholesale & retail | 2017 |
| Knight Restaurant Limited | Hospitality | 2018 |
| Knight-Beaton Properties Ltd | Construction | 2024 |
| Knipes & Co Ltd | Wholesale & retail | 2021 |
| Knock on Wood Gower Ltd | Construction | 2026 |
| Knockweed Ltd | Administrative & support | 2024 |
| Knotweed Control Swansea Ltd | Administrative & support | 2015 |
| Knoxinator Ltd | Health & social care | 2023 |
| KO Gym Limited | Arts & recreation | 2020 |
| Koba Properties Limited | Real estate | 2021 |
| Kodavell Group Limited | Construction | 2025 |
| Koinonia Studio Ltd | Arts & recreation | 2022 |
| Konnexted Ltd | Wholesale & retail | 2024 |
| Konshush Design Limited | Professional & scientific | 2019 |
| Kookaburra Assets Ltd | Construction | 2026 |
| Koop and Kiln Ltd | Agriculture & fishing | 2024 |
| Koraw Ltd | Wholesale & retail | 2019 |
| Koreana Travel Ltd | Administrative & support | 2024 |
| Korekar Limited | Information & communication | 2026 |
| Kornchain Limited | Information & communication | 2018 |
| Koru Ecology Associates Ltd | Professional & scientific | 2022 |
| Koudai Limited | Real estate | 2006 |
| KP Marine Industries Ltd | Transport & logistics | 2025 |
| KPA Consulting Engineers Limited | Professional & scientific | 2008 |
| KPG Brickwork Ltd | Construction | 2021 |
| Kraftzone Ltd | Manufacturing | 2023 |
| KRC Property Limited | Real estate | 2024 |
| Kreative Hospitality Ltd | Hospitality | 2018 |
| KRF Event Catering Ltd | Hospitality | 2024 |
| KRH Construction Project Management Ltd | Professional & scientific | 2026 |
| Krislyn Motors Limited | Wholesale & retail | 1975 |
| Krisola Limited | Information & communication | 2018 |
| Kristal Property Ltd | Real estate | 2024 |
| Krols Brothers Ltd | Construction | 2015 |
| Kronos Energy Solutions Ltd | Professional & scientific | 2024 |
| Kross Design Ltd | Manufacturing | 2025 |