| JMW Software Ltd | Professional & scientific | 2026 |
| JN Capital Holdings Ltd | Real estate | 2025 |
| JNC Interiors Kitchens & Bathrooms Ltd | Construction | 2022 |
| JNH Swansea Limited | Wholesale & retail | 2024 |
| JO Macauley Ltd | Information & communication | 2020 |
| JO Wood Legal Limited | Professional & scientific | 2025 |
| Jo-Ann Cahill Group Ltd | Professional & scientific | 2025 |
| Jobodo Ltd. | Administrative & support | 2015 |
| Jocaravan Ltd | Hospitality | 2026 |
| JOE Elliot Electrical & Renewables Ltd | Construction | 2023 |
| Joe's EYE Screen Limited | Health & social care | 2008 |
| Joe-Cam Limited | Hospitality | 2000 |
| Joeboy Tattoo Ltd | Arts & recreation | 2025 |
| Joel Matuschke Electrical Ltd | Construction | 2026 |
| Joel Redman Limited | Professional & scientific | 2015 |
| Joes Pizza & Kebabs Ltd | Hospitality | 2024 |
| Joes Swansea Limited | Hospitality | 2019 |
| Johal Estates Ltd | Real estate | 2017 |
| John Baker Engineering Ltd | Professional & scientific | 2024 |
| John Collins & Partners LLP | | 2004 |
| John Edwards Funeral Directors Limited | Other services | 2007 |
| John F. Harvey Ltd | Professional & scientific | 2003 |
| John Glen (Installation Services) Limited | Construction | 1998 |
| John H Wright Limited | Professional & scientific | 2010 |
| John M Grainger Limited | Professional & scientific | 2009 |
| John Mcentee Ltd | Real estate | 1959 |
| John Mitchell Electrical Solutions Limited | Construction | 2026 |
| John Phillips Financial Planning LLP | | 2014 |
| John Rickard (Autos) Limited | Administrative & support | 1978 |
| John Rickard Motor Factors Limited | Wholesale & retail | 2004 |
| John Roberts Properties Ltd | Real estate | 2017 |
| John Stephens Services Ltd | Administrative & support | 1975 |
| John Weaver (Holdings) Limited | Construction | 1996 |
| John X - Mechwind Ltd | Manufacturing | 2020 |
| Johnnies Fish & Chips Ltd | Wholesale & retail | 2023 |
| Johns & Co Homes Ltd | Real estate | 2025 |
| Johnson Hall Environmental Limited | Administrative & support | 2009 |
| Johnson Hall Services Limited | Wholesale & retail | 1998 |
| Johnson, Hall & Company Limited | Construction | 1984 |
| Johnsons Engineering Ltd | Professional & scientific | 2022 |
| Johnson`S Retail Limited | Administrative & support | 2007 |
| JOI Solutions Limited | Construction | 2013 |
| Joinery Connection Limited | Construction | 2025 |
| JOL Property Ltd | Real estate | 2024 |
| Jolex Limited | Administrative & support | 2017 |
| Jolly FUN Ltd | Information & communication | 2020 |
| JON Ball Plastering & Renovations Ltd | Construction | 2023 |
| JON Leahy Maintenance Ltd | Real estate | 2026 |
| JON Will Consult Limited | Professional & scientific | 2017 |
| Jonah Ward Services Ltd | Construction | 2016 |
| Jonaki Tandoori Limited | Hospitality | 2020 |
| Jonathan Davies Limited | Other services | 1994 |
| Jonathan Hughes Limited | Professional & scientific | 2016 |
| Jonathan Morgan Properties Ltd | Real estate | 2018 |
| Jones & Jones Electrical Limited | Construction | 2017 |
| Jones & Sons Butchers Ltd | Wholesale & retail | 2018 |
| Jones Assets Limited | Real estate | 2024 |
| Jones Brothers (Ammanford) Limited | Real estate | 1947 |
| Jones Ecology Ltd | Professional & scientific | 2020 |
| Jones Giles Limited | Financial services | 2006 |
| Jones Health, Fitness and Lifestyle Ltd | Education | 2023 |
| Jones Landscapes Limited | Administrative & support | 2019 |
| Jones Property Group Holdings Ltd | Financial services | 2025 |
| Jones Swansea Limited | Real estate | 2011 |
| Jones-Knight Coffee Ltd | Hospitality | 2024 |
| Jonny Hutch Engineering Ltd | Professional & scientific | 2022 |
| Jonsil Bricklaying Contractors Ltd | Construction | 2013 |
| Jopo Customs Ltd | Wholesale & retail | 2017 |
| Jopofest Limited | Arts & recreation | 2024 |
| Jordan JOE Welding Co Ltd | Manufacturing | 2025 |
| Jordan L Jones Limited | Education | 2024 |
| Jorosar Property 2 Limited | Real estate | 2021 |
| Jorosar Property Limited | Real estate | 2022 |
| Josef Herman Art Foundation Cymru Trust Limited | Arts & recreation | 2003 |
| Joseph and Thomas Food Group Limited | Wholesale & retail | 2017 |
| Joseph Digs Ltd | Real estate | 2025 |
| Josephine and Daniella Ltd | Other services | 2016 |
| Josephine Optometry Limited | Health & social care | 2022 |
| Josey Global Limited | Mining & quarrying | 2026 |
| Joshua's Barber Shop Limited | Other services | 2009 |
| Josie Way Investments Ltd | Administrative & support | 2013 |
| Josilliam Ltd | Construction | 2016 |
| Journey Electrical Ltd | Construction | 2025 |
| JOURNEY2JANNAH Ltd | Administrative & support | 2025 |
| Jowills Ltd | Professional & scientific | 2014 |
| Joxen Limited | Other services | 2023 |
| Joy Transformation International Academy Limited | Education | 2022 |
| Joyce Property Management Limited | Real estate | 2025 |
| Joyfulclicks Ltd | Professional & scientific | 2025 |
| Joyneli Limited | Wholesale & retail | 2025 |
| JP BID Writing Ltd | Administrative & support | 2026 |
| JP Cleaners Ltd | Administrative & support | 2024 |
| JP Construction & Development Ltd | Construction | 2010 |
| JP Construction (Swansea) Limited | Financial services | 2023 |
| JP Construction and Design Limited | Real estate | 2003 |
| JP Decorators Ltd | Construction | 2024 |
| JP Installations Ltd | Construction | 2022 |
| JP Land & Property Ltd | Real estate | 2026 |
| JP Landscaping & Gardening Ltd | Administrative & support | 2024 |
| JP Property Development Ltd | Real estate | 2024 |