| IL Engineering Limited | Professional & scientific | 2017 |
| IL Property Limited | Real estate | 2019 |
| IMC Film & TV Tracking Vehicle Services Ltd | Information & communication | 2015 |
| IN the Womb Limited | Information & communication | 2011 |
| Incredible Edible Carmarthenshire CIC | Agriculture & fishing | 2020 |
| Individual Solutions Ltd | Professional & scientific | 2016 |
| Indroy Limited | Households | 2008 |
| Industrial & Marine Services Ltd | Manufacturing | 2022 |
| Inet Experts Limited | Professional & scientific | 1997 |
| Inhale Anaesthesia Ltd | Education | 2026 |
| Innagen Limited | Professional & scientific | 2025 |
| Innovative Resource Solutions Ltd | Professional & scientific | 2022 |
| Insall Consulting Limited | Information & communication | 2018 |
| Inspector Pipes Limited | Wholesale & retail | 2015 |
| Inspire Wellbeing - TAI CHI Qigong Ltd | Health & social care | 2025 |
| Inspired to Soar Ltd | Other services | 2016 |
| Instinct IRM Limited | Financial services | 2020 |
| Integral Actor Limited | Arts & recreation | 2012 |
| Intelligencenet Limited | Information & communication | 2006 |
| Intelligent Care Planning Limited | Administrative & support | 2023 |
| Intelligent Care Systems Ltd | Administrative & support | 2023 |
| Introsport UK Limited | Education | 2007 |
| IQ Fleet Solutions Limited | Wholesale & retail | 1999 |
| IRL Games Ltd | Arts & recreation | 2022 |
| Ironclad Hire Ltd | Administrative & support | 2025 |
| Isyx Property Group Limited | Real estate | 2025 |
| It's an ACT Ltd | Arts & recreation | 2011 |
| Itasty Limited | Hospitality | 2017 |
| IVY Nova Ltd | Hospitality | 2024 |
| Iwan Rees Accountancy Limited | Professional & scientific | 2013 |
| Iwec International Limited | Construction | 2000 |
| J & J Motors Limited | Wholesale & retail | 1998 |
| J & L Lettings Limited | Real estate | 2020 |
| J & P Properties (Swansea) Limited | Construction | 2015 |
| J & S Landscaping & Tree Services Ltd | Administrative & support | 2016 |
| J B Plant & Groundwork Services Limited | Administrative & support | 2016 |
| J C L Car Sales Limited | Wholesale & retail | 2008 |
| J C Snooker Academy Ltd | Arts & recreation | 2025 |
| J E Thomas of Llangennech Limited | Construction | 2003 |
| J H Woodall Builders Limited | Construction | 2019 |
| J J Fishers Ltd | Transport & logistics | 2020 |
| J Lewis Lettings Ltd | Real estate | 2026 |
| J M D Flooring Limited | Wholesale & retail | 2016 |
| J R Events Promotions Ltd | Hospitality | 2011 |
| J Randall Roofing Contractors Limited | Construction | 2010 |
| J Rees Building Limited | Construction | 2020 |
| J Williams Property Management Ltd | Construction | 2025 |
| J&S Property Flips Limited | Real estate | 2025 |
| J. W and Sons' Services Limited | Manufacturing | 2020 |
| J.Allegri and SON Limited | Construction | 1947 |
| J.B. Jenkins & SON Limited | Hospitality | 1978 |
| J.Ferreira Ltd | Health & social care | 2014 |
| J.M. Thomas Property Solutions Ltd | Construction | 2019 |
| J.R. Anthony (Haulage) Limited | Transport & logistics | 1968 |
| J.W. Shipping Limited | Transport & logistics | 1996 |
| Jabiru Databases Applications Reports Ltd | Information & communication | 2015 |
| JAC Daniel Cars Limited | Wholesale & retail | 2025 |
| Jacob Martin Films CYF | Information & communication | 2023 |
| Jade & Sons (Plumbing & Heating) Limited | Construction | 2007 |
| Jael Property Limited | Real estate | 2025 |
| Jaflong Spicy Limited | Hospitality | 2025 |
| Jamie Clarke Snooker Academy C.I.C. | Arts & recreation | 2025 |
| Jamie Smith Properties Limited | Real estate | 2026 |
| Janet Waldron Education Support Ltd | Education | 2020 |
| JAS Coffee Limited | Hospitality | 2023 |
| Jazzbones Ltd | Real estate | 2023 |
| JB Plant & Co Groundwork Services Ltd | Construction | 2023 |
| JCC Solutions Ltd | Professional & scientific | 2023 |
| Jcfj Ltd | Wholesale & retail | 2015 |
| JCR Planning & Design Ltd | Professional & scientific | 2025 |
| JCR Planning Limited | Professional & scientific | 2014 |
| JDT Developments Limited | Construction | 2003 |
| JE Lead Consultancy Limited | Professional & scientific | 2025 |
| Jenkins Garden Machinery Limited | Wholesale & retail | 2010 |
| Jenx Plant Limited | Agriculture & fishing | 2014 |
| Jesse Aerotech Limited | Manufacturing | 2015 |
| JFM Property Group Ltd | Real estate | 2026 |
| JG Landscapes Ltd | Construction | 2025 |
| Jjbautocare Ltd | Wholesale & retail | 2025 |
| JK Mobile Caravan Servicing and Repairs Limited | Manufacturing | 2012 |
| JL Hurley Investments Ltd | Financial services | 2026 |
| JMJ Harmony Ltd | Health & social care | 2023 |
| JMS Bars Ltd | Hospitality | 2025 |
| JOB Dunne Properties Ltd | Households | 2025 |
| Joeco Assets Ltd | Financial services | 2026 |
| Joeco Holdings Ltd | Administrative & support | 2026 |
| Joeco Properties Ltd | Real estate | 2026 |
| John Evans & Sons(Llanelli)Limited | Transport & logistics | 1954 |
| John Jenkins Painters Limited | Construction | 2010 |
| John Treharne Engineering Limited | Manufacturing | 2017 |
| Johnson Bros. Coal Factors Limited | Wholesale & retail | 1963 |
| Johnson Bros. Properties Limited | Real estate | 2017 |
| Joio JAC Limited | Manufacturing | 2013 |
| Jollies on the Hilltop Limited | Hospitality | 2019 |
| Jonah Properties Ltd | Real estate | 2021 |
| Jonathan Thomas Decorators Limited | Construction | 2022 |
| Jones Plastering Solutions Ltd | Construction | 2019 |
| Jones Sport & Performance Vehicles Ltd | Wholesale & retail | 2018 |
| Jonesport Rally Hire Limited | Manufacturing | 2020 |
| Jonny Clayton Darts Limited | Arts & recreation | 2017 |