| J.A.N. Limited | Health & social care | 1988 |
| J.D. Plant Services Limited | Administrative & support | 1999 |
| J.H.Donovan & SON Limited | Wholesale & retail | 1946 |
| J.H.F. (1985) Limited | Real estate | 1959 |
| J.H.Lidstone(Plastering)Limited | Construction | 1963 |
| J.J Associates Distribution Limited | Wholesale & retail | 1999 |
| J.Miller Marketing Ltd | Wholesale & retail | 2026 |
| J.S. Spurrell Property Developments Limited | Real estate | 1985 |
| J.T. Gibbs & Co. Limited | Real estate | 1946 |
| J.Utileyties Ltd | Construction | 2025 |
| JA Mcpherson Limited | Professional & scientific | 2015 |
| JAA Engineering Limited | Financial services | 2024 |
| Jabal Marra Ltd | Wholesale & retail | 2017 |
| Jabs Medical South West Ltd | Health & social care | 2021 |
| JAC Electrical SW Limited | Construction | 2013 |
| JAC the App Ltd | Information & communication | 2022 |
| Jacalyn James Limited | Education | 2020 |
| Jack Alexander Bricklayers Ltd | Construction | 2021 |
| Jack and EVE Fishing Limited | Agriculture & fishing | 2026 |
| Jack Hawkins Limited | Manufacturing | 2017 |
| Jack James Engineering Limited | Professional & scientific | 2025 |
| Jack Lawrence Financial Services Limited | Real estate | 1985 |
| Jack Stoneman Scaffolding Limited | Construction | 2014 |
| Jack TAR Ltd | Professional & scientific | 2013 |
| Jackamax Limited | Agriculture & fishing | 2012 |
| Jackson Landscaping Limited | Wholesale & retail | 2021 |
| Jackson's Gym Plymouth Ltd | Arts & recreation | 2022 |
| Jackson's Spotless Solutions Ltd | Administrative & support | 2025 |
| Jacob Cattrall Ltd | Information & communication | 2018 |
| Jadeb Associates Limited | Construction | 2014 |
| Jafal Ltd | Construction | 2025 |
| Jagaban of Plymouth Entertainment Ltd | Information & communication | 2024 |
| Jaguar Joinery Limited | Extraterritorial | 2018 |
| Jaguar Project Consulting Ltd Ltd | Information & communication | 2018 |
| JAK Thomas Ltd | Administrative & support | 2016 |
| Jalayi Limited | Wholesale & retail | 2024 |
| Jalwa Indian Bistro Ltd | Hospitality | 2025 |
| JAM Engineering Solutions Ltd | Professional & scientific | 2023 |
| Jambo Support Limited | Health & social care | 2019 |
| James Brothers Funeral Directors Limited | Other services | 2014 |
| James Building and Developments Ltd | Construction | 2025 |
| James Consultancy (SW) Ltd | Professional & scientific | 2019 |
| James Edgar Design Ltd | Professional & scientific | 2014 |
| James Green Group Ltd | Financial services | 2018 |
| James Green Holdings Limited | Financial services | 2016 |
| James Green Investments Limited | Real estate | 2017 |
| James Green Limited | Wholesale & retail | 2013 |
| James Hewitt Furniture by Design Limited | Manufacturing | 2022 |
| James Johnson Green Limited | Wholesale & retail | 2016 |
| James L. Nash Limited | Real estate | 1943 |
| James Marshall Property Ltd | Real estate | 2024 |
| James Property Management (SW) Ltd | Real estate | 2021 |
| James Pryce London Ltd | Other services | 2012 |
| James Taylor Editor Ltd | Information & communication | 2017 |
| James Ward Engineering Ltd | Manufacturing | 2019 |
| James Wells Planning Limited | Professional & scientific | 2012 |
| Jamron Media Ltd | Information & communication | 2014 |
| JAN O'Neill Mortgages Limited | Financial services | 2012 |
| Jane & James Ltd | Administrative & support | 2022 |
| Jane Chipp Art Limited | Wholesale & retail | 2026 |
| Jane Lewis Consulting Limited | Professional & scientific | 2025 |
| Janey Howl Ltd | Health & social care | 2022 |
| Janners Sports Bar Limited | Hospitality | 2024 |
| JAO247 Limited | Health & social care | 2023 |
| Japhetiva Limited | Public administration | 2025 |
| JAR Plymouth Limited | Wholesale & retail | 2019 |
| Jarg Holdings Limited | Financial services | 2025 |
| Jarsquad CIC | Manufacturing | 2021 |
| Jarvis Consultancy Limited | Professional & scientific | 1995 |
| Jarvis Nuclear Limited | Professional & scientific | 2017 |
| JAS Quantity Surveyors Limited | Professional & scientific | 2021 |
| Jasi Company (UK) Limited | Wholesale & retail | 2012 |
| Jask Property Maintenance Ltd | Construction | 2014 |
| Jasminelouise Consultancy Ltd | Information & communication | 2025 |
| Jason Carlisle Recruitment Ltd | Administrative & support | 2025 |
| Jason Hyne Limited | Administrative & support | 2003 |
| Jason Moyle Racing Ltd | Wholesale & retail | 2023 |
| Jasper LM Ltd | Hospitality | 2019 |
| Jass Commercial Cleaners Ltd | Administrative & support | 2021 |
| Javaconstruction Ltd | Construction | 2021 |
| JAX Car Breakers Limited | Water & waste | 2026 |
| JAY Consultancy Plymouth Ltd | Professional & scientific | 2015 |
| Jay's Building & Renovations Limited | Construction | 2025 |
| Jay's Properties and Developments Ltd | Real estate | 2019 |
| Jay's Rental Properties Ltd | Real estate | 2025 |
| Jay's Scrap & Waste Management Ltd | Water & waste | 2011 |
| Jay's Scrapyard Ltd | Water & waste | 2025 |
| Jaya Pathivara Limited | Wholesale & retail | 2024 |
| Jayb Consultancy Ltd | Extraterritorial | 2025 |
| Jays Container Ltd | Wholesale & retail | 2018 |
| Jays Mastics Limited | Construction | 2017 |
| Jayseats Ltd | Hospitality | 2021 |
| Jazmin Ltd | Hospitality | 2020 |
| JB Compass Developments Ltd | Construction | 2025 |
| JB MED Ltd | Health & social care | 2024 |
| JB Plumbing (SW) Limited | Construction | 2006 |
| JB Plumbing Devon & Cornwall Ltd | Construction | 2021 |
| JBA Couriers Ltd | Extraterritorial | 2015 |
| JBK Courier Services Ltd | Transport & logistics | 2023 |
| JC Account Trading Ltd | Administrative & support | 2025 |