| HT Electrical and Carpentry Ltd | Construction | 2020 |
| HT Plumbing & Heating Ltd | Construction | 2019 |
| Hughes Business Services Limited | Information & communication | 2006 |
| HWB Helpu CYF. | Health & social care | 2020 |
| Hydroinformatics Limited | Professional & scientific | 2010 |
| Hywel Anthony Estate Agents Ltd | Real estate | 2014 |
| Hywels Happy Hounds Limited | Other services | 2025 |
| I.M.S Electrical & Security Limited | Construction | 2024 |
| IAI Solutions Ltd | Professional & scientific | 2015 |
| IAN Williams Carpentry Limited | Construction | 1999 |
| IDA Grow Limited | Wholesale & retail | 2026 |
| Ifeson Limited | Real estate | 2023 |
| Images Design Print & Embroidery Limited | Manufacturing | 2008 |
| Impressions Dental Laboratories Limited | Manufacturing | 2023 |
| Inclusion Included Limited | Professional & scientific | 2020 |
| Index Waterproofing Technology UK Ltd | Construction | 2010 |
| Infinity Hair (Pontyclun) Ltd | Other services | 2022 |
| INK Signage Experts Limited | Professional & scientific | 2020 |
| Inmyestimation Limited | Professional & scientific | 2019 |
| Inspiring Business Growth Ltd | Administrative & support | 2021 |
| Intervention Developments Ltd | Real estate | 2014 |
| Intervention Services Limited | Construction | 2002 |
| Intervention Utilities Ltd | Construction | 2010 |
| Introbiz Franchising Ltd | Hospitality | 2018 |
| Ipmo Limited | Information & communication | 2014 |
| IPW Climatech Ltd | Construction | 2025 |
| IPW Properties Ltd | Real estate | 2025 |
| Iron Horse Recoveries Ltd | Wholesale & retail | 2026 |
| Isaac Affiliates Ltd | Health & social care | 2017 |
| IT Repairs Limited | Other services | 2009 |
| IW Carpentry Holdings Ltd | Financial services | 2025 |
| J Evans Limited | Education | 2010 |
| J P Windows & Conservatories Limited | Construction | 2000 |
| J T Carpentry (South Wales) Ltd | Manufacturing | 2024 |
| J.E.T. Developments Limited | Construction | 2004 |
| J.H. Leeke and Sons Limited | Professional & scientific | 2004 |
| Jackie Lewis (Training & Consultancy) Services Ltd | Professional & scientific | 2009 |
| Jade Canton Limited | Hospitality | 2024 |
| Jafran Indian Cuisine Ltd | Hospitality | 2025 |
| Jask Projects Limited | Construction | 1987 |
| Jayne Morris Estate Agent Limited | Real estate | 2025 |
| Jay`S Sewing Machine Repairs Limited | Manufacturing | 2006 |
| Jazzy Jungle Ltd | Arts & recreation | 2016 |
| JC Heating and Plumbing Green Ltd | Construction | 2011 |
| JCD Enterprises Ltd | Extraterritorial | 2024 |
| JCG Construction Limited | Construction | 2019 |
| JCH Exterior Cleaning Specialists Ltd | Administrative & support | 2026 |
| JDD Medical Ltd | Health & social care | 2021 |
| Jelly Turtle Limited | Wholesale & retail | 2015 |
| Jellybean TV & Film Ltd | Professional & scientific | 2023 |
| Jewelled Phoenix Ltd | Manufacturing | 2022 |
| Jewellery Academy Wales Ltd | Manufacturing | 2021 |
| JF Groundworks Ltd | Construction | 2025 |
| JH Facilities Management Limited | Administrative & support | 2019 |
| JJ & SON Deliveries Limited | Transport & logistics | 2007 |
| JJ Real Estate Investments Limited | Real estate | 2023 |
| JLC Drylining Ltd | Construction | 2022 |
| JLJ Network Ltd | Administrative & support | 2026 |
| JM Construction Workers Ltd | Construction | 2025 |
| JMB Carpentry & Landscaping Ltd | Construction | 2026 |
| JMP Group Limited | Construction | 2015 |
| JMT Music Services Ltd | Education | 2017 |
| JN Building Services & Property Development Limited | Construction | 2025 |
| Jolly Jesters Ltd | Arts & recreation | 2015 |
| JON Thomas Windows Ltd | Construction | 2021 |
| Jones Food & Beverage Ltd | Hospitality | 2017 |
| Jones Power & Construction Ltd | Construction | 2026 |
| Jonesy Mechanical Services Ltd | Professional & scientific | 2025 |
| Jordan Civils (Wales) Ltd | Construction | 2012 |
| Joshua Stratford Health & Safety Ltd | Construction | 2024 |
| JRA Dean Ltd | Real estate | 2025 |
| JRG Pharm Locum Ltd | Wholesale & retail | 2025 |
| JRR Developments Limited | Real estate | 2020 |
| Jtec Equipment Limited | Mining & quarrying | 2016 |
| Just Prospr Limited | Information & communication | 2024 |
| K & C Pearce Limited | Construction | 2014 |
| K & J Motors Pontyclun Limited | Wholesale & retail | 2009 |
| K B P M Limited | Information & communication | 2008 |
| K. Jones Roofing Limited | Construction | 1994 |
| K.J. Walby Limited | Wholesale & retail | 2001 |
| K1 Estates Limited | Real estate | 2016 |
| K1 Logistics Ltd | Transport & logistics | 2009 |
| Kale Psychology Practice Ltd | Health & social care | 2023 |
| Kalimani Limited | Professional & scientific | 2025 |
| Kalrav Limited | Professional & scientific | 2018 |
| Karma Card Co Ltd | Manufacturing | 2025 |
| Karma Krafts Ltd | Manufacturing | 2023 |
| Katering Twocann Limited | Hospitality | 2016 |
| Keezys Customs Limited | Wholesale & retail | 2026 |
| Kerry Jenkins Roofing Ltd | Construction | 2022 |
| Kgreaves Holdings Limited | Wholesale & retail | 2024 |
| Khurram 786 Ltd | Wholesale & retail | 2025 |
| Kidd and Sons Ltd | Real estate | 2023 |
| KIM Williams GAS & SON Ltd | Wholesale & retail | 2024 |
| Kineric Homes Limited | Real estate | 2019 |
| Kinsey Security Limited | Administrative & support | 2019 |
| KL Bespoke Developments Ltd | Real estate | 2025 |
| KLM Hotels Ltd | Hospitality | 2024 |
| KLT Holdings Ltd | Financial services | 2025 |
| KLT Property & Maintenance Specialists Ltd | Construction | 2024 |