| Juicecraft Ltd | Wholesale & retail | 2025 |
| Juicypepperz Ltd | Manufacturing | 2021 |
| Juicyvox Ltd | Information & communication | 2025 |
| Juju Property and Investments Ltd | Real estate | 2022 |
| Jukebox Collective | Arts & recreation | 2013 |
| Julcris Property Limited | Construction | 2018 |
| Julia Brooker Paintings Limited | Arts & recreation | 2009 |
| Julia Clark Beauty Centre Ltd | Other services | 2018 |
| Julian Healthcare Ltd | Health & social care | 2018 |
| Julian Hodge Bank Limited | Financial services | 1962 |
| Julian Hodge Finance Limited | Professional & scientific | 1989 |
| Julian Hodge Limited | Professional & scientific | 1999 |
| Julian Sweetman MLE Limited | Health & social care | 2016 |
| Juliano Group Ltd | Manufacturing | 2020 |
| Juliet Mart Ltd | Wholesale & retail | 2025 |
| Julishiny International Holding Group Co., Ltd | Extraterritorial | 2019 |
| Julius Gabris Ltd | Transport & logistics | 2016 |
| Julsmak Limited | Wholesale & retail | 2020 |
| Jumany Ltd | Wholesale & retail | 2013 |
| Jumble Media Ltd | Information & communication | 2026 |
| Jumblelogic Limited | Hospitality | 1988 |
| Jumbo Europe Ltd | Wholesale & retail | 2020 |
| Jumbo Mumbo Ltd | Wholesale & retail | 2025 |
| Jumper Network Co., Ltd | Extraterritorial | 2021 |
| Jumping Jack Darts Limited | Information & communication | 2024 |
| Jumpstartdigital UK Ltd | Information & communication | 2024 |
| Junaid Travels Ltd | Transport & logistics | 2019 |
| Junaih Ltd | Wholesale & retail | 2025 |
| Junction Autos Ltd | Wholesale & retail | 2019 |
| June Construction Limited | Construction | 2015 |
| Junearc 1991 Limited | | 1982 |
| Juneluc Electrical Co., Ltd | Manufacturing | 2025 |
| Jungi Properties LLP | | 2024 |
| Jungi Property Developments Limited | Real estate | 2025 |
| Jungle Mania Soft Play Ltd | Arts & recreation | 2014 |
| Jungle Nightclub Limited | Hospitality | 2019 |
| Junior Kuppanna Ltd | Hospitality | 2022 |
| Junior Walker Limited | Wholesale & retail | 2020 |
| Juniper Retail Ltd | Wholesale & retail | 2025 |
| Juniusapp Ltd | Information & communication | 2024 |
| Junksbin Limited | Wholesale & retail | 2025 |
| Junlihang International Limited | Professional & scientific | 2012 |
| Juno (Cardiff) Limited | Administrative & support | 2019 |
| Juno Resourcing Ltd | Information & communication | 2021 |
| Junseven Limited | Wholesale & retail | 2020 |
| Junwan Trading Co., Ltd | Wholesale & retail | 2021 |
| Jupe Arts Ltd | Wholesale & retail | 2019 |
| Jupe Industries Ltd | Information & communication | 2025 |
| Jupi Express Limited | Wholesale & retail | 2025 |
| Jupiter Cardiff Limited | Real estate | 2013 |
| Jupiter House Limited | Real estate | 2017 |
| Jupiter Maintenance Limited | Administrative & support | 2023 |
| Jupiter New Business Ltd | Administrative & support | 2015 |
| Jupiter-Fd Ltd | Professional & scientific | 2025 |
| Jupmar Limited | Other services | 2014 |
| Jurassic Virtual Reality Developments Limited | Professional & scientific | 2014 |
| Juris International Ltd | Information & communication | 2022 |
| Jurmin Co., Ltd | Wholesale & retail | 2021 |
| JUS Global (Holdings) Limited | Information & communication | 2026 |
| JUS Global UK Ltd | Information & communication | 2026 |
| JUS Magic Limited | Wholesale & retail | 2018 |
| Jushi Body Kits Ltd. | Manufacturing | 2018 |
| Just a Bargain Online Limited | Wholesale & retail | 2020 |
| Just a Scratch Ltd | Other services | 2017 |
| Just Accounts (Cardiff) Ltd | Professional & scientific | 2014 |
| Just Air (Services) Limited | Energy | 2012 |
| Just Airport Cardiff Limited | Transport & logistics | 2019 |
| Just BE YOU Intervention CIC | Manufacturing | 2024 |
| Just BEE Loved Ltd | Manufacturing | 2014 |
| Just Builders Services Ltd | Construction | 2016 |
| Just Call Mortgages & Loans Ltd | Financial services | 2004 |
| Just Druid Creative Ltd | Information & communication | 2021 |
| Just Druid Holdings Ltd | Information & communication | 2021 |
| Just Funky UK Ltd | Wholesale & retail | 2022 |
| Just Glaze Windows & Doors Limited | Wholesale & retail | 2020 |
| Just Great Service Ltd | Construction | 2024 |
| Just Groceries Plus Limited | Wholesale & retail | 2023 |
| Just Hospitality Talent Ltd | Other services | 2019 |
| Just Host IT Ltd | Wholesale & retail | 2020 |
| Just Lofts & Build Limited | Manufacturing | 2025 |
| Just Lofts (Loft Specialists) Ltd | Construction | 2022 |
| Just More Value Limited | Wholesale & retail | 2018 |
| Just Mortgages (Sussex) Limited | Financial services | 2017 |
| Just MOT & Repair Limited | Wholesale & retail | 2014 |
| Just Painters Solutions Ltd | Administrative & support | 2017 |
| Just Paranoid Ltd | Information & communication | 2023 |
| Just Perfect Catering Limited | Hospitality | 2009 |
| Just Pure Ltd | Professional & scientific | 2014 |
| Just Rails Limited | Construction | 2003 |
| Just Scaffolding (S. Wales) Ltd | Construction | 2016 |
| Just Skin Beauty Ltd | Other services | 2022 |
| Just Tankers Holdings Ltd | Water & waste | 2020 |
| Just Tankers Road Tanker Ltd | Water & waste | 2020 |
| Just VMA Limited | Wholesale & retail | 2019 |
| Just YOU and I Ltd | Hospitality | 2021 |
| Justapps Ltd | Professional & scientific | 2018 |
| Justappsec Limited | Information & communication | 2025 |
| Justice, Inclusion, and Support Team (Jist) C.I.C. | Health & social care | 2025 |
| Justice.Wales Legal Clinic CIC | Professional & scientific | 2025 |
| Justin Beavis Limited | Professional & scientific | 2021 |