| Janidade Services Limited | Administrative & support | 2002 |
| Janmat Building Ltd | Construction | 2022 |
| Janmat Construction Ltd | Construction | 2022 |
| Jann Ltd | Wholesale & retail | 2018 |
| Jantke Property Ltd | Real estate | 2025 |
| Jarn Group Ltd | Construction | 2022 |
| Jaseur Limited | Information & communication | 2000 |
| Jaskulla Mentoring CIC | Education | 2024 |
| Jasmine Desai Optical Limited | Wholesale & retail | 2022 |
| Jasmine Quality Care Services Ltd | Health & social care | 2024 |
| Jason Currill Coaching Limited | Other services | 2024 |
| Jason Mcguigan Ltd | Financial services | 2009 |
| Javed Real Estate Limited | Real estate | 2021 |
| JAY Hair and Cosmetics Ltd | Wholesale & retail | 2025 |
| Jaya Luxmi Ltd | Hospitality | 2025 |
| Jayg Ltd | Transport & logistics | 2023 |
| Jaykay Futures Ltd | Education | 2008 |
| Jayma Ltd | Real estate | 2024 |
| Jays Sameday Couriers Ltd | Transport & logistics | 2025 |
| Jaysmith Limited | Real estate | 1963 |
| JB Management and Consultancy Services Ltd | Professional & scientific | 2008 |
| JBB Management Consulting Ltd | Professional & scientific | 2016 |
| JBC Domestic Services Limited | Administrative & support | 2024 |
| JBS Joni Building Services Ltd | Construction | 2025 |
| Jbwh Communications Limited | Professional & scientific | 2018 |
| JC Taxi Hire Ltd | Transport & logistics | 2025 |
| Jc.Historics Limited | Administrative & support | 2009 |
| JCB (UK) Limited | Construction | 2014 |
| JCB Cleaning Services Limited | Administrative & support | 2026 |
| JCH Care Limited | Health & social care | 2024 |
| JCK Films LLP | | 2010 |
| JCM Systems Limited | Information & communication | 2012 |
| Jcnc Machine Service Limited | Manufacturing | 2010 |
| JCS Online Resources Limited | Education | 2010 |
| Jcsupplied Ltd | Wholesale & retail | 2025 |
| JCW Foods Ltd | Wholesale & retail | 2019 |
| JD Bathrooms & Kitchens Limited | Wholesale & retail | 2016 |
| JD Biomedical Solutions Ltd | Professional & scientific | 2014 |
| JD Properties (Wyboston) Ltd | Real estate | 2022 |
| JDC Property and Development Limited | Real estate | 2024 |
| JDP Science Limited | Professional & scientific | 2016 |
| JDW Hydraulics Ltd | Manufacturing | 2018 |
| Jeff Farrow Associates Limited | Professional & scientific | 2010 |
| Jeff JEN Care Plus Limited | Real estate | 2014 |
| JEL Business Process Improvement Limited | Professional & scientific | 2012 |
| Jemjoy Care Ltd | Health & social care | 2018 |
| Jems Limited | Other services | 1952 |
| Jenner Vaccine Foundation | Professional & scientific | 1995 |
| Jennings (Containers & Storage) Limited | Transport & logistics | 1993 |
| Jennings Business Park Limited | Real estate | 2024 |
| Jenny Harvey Immigration Limited | Professional & scientific | 2016 |
| JEO Limited | Wholesale & retail | 2020 |
| JEP Decorating Ltd | Construction | 2026 |
| Jera Consulting Limited | Professional & scientific | 2007 |
| Jericho Alignment Infrastructure | Professional & scientific | 2024 |
| Jericho Cheese Company Ltd. | Wholesale & retail | 2016 |
| Jericho Coffee Traders Limited | Wholesale & retail | 2014 |
| Jericho Community Boatyard Limited | Other services | 2006 |
| Jericho Hospitality Ltd | Hospitality | 2023 |
| Jericho Living Heritage Trust | Education | 2008 |
| Jericho Productions Limited | Information & communication | 2021 |
| JES Care Services Limited | Health & social care | 2015 |
| Jessamine Leonora Limited | Administrative & support | 2016 |
| Jessamy Healthcare Limited | Health & social care | 2014 |
| Jessie Anand Productions Ltd | Arts & recreation | 2018 |
| Jessop and Cook Architects Ltd. | Professional & scientific | 2000 |
| Jesus College Ball Limited | Arts & recreation | 2026 |
| Jesus College Developments (Oxford) Limited | Construction | 2017 |
| Jesvana Ltd | Administrative & support | 2022 |
| Jewell & Co Limited | Professional & scientific | 2011 |
| Jewson Film Productions Limited | Information & communication | 2005 |
| JEZ Webb Ltd | Wholesale & retail | 2010 |
| Jezzam Limited | Other services | 2010 |
| JF Boxing Limited | Professional & scientific | 2023 |
| JF Group Holdings Ltd | Wholesale & retail | 2024 |
| JF Office Interiors Limited | Wholesale & retail | 2011 |
| JG Klick Ltd | Real estate | 2018 |
| JG Nutritional Services Limited | Health & social care | 2020 |
| JG Sports Enterprises Ltd | Professional & scientific | 2018 |
| JGS Butchery & Grocery Shop Ltd | Wholesale & retail | 2018 |
| Jiamart Oxford Ltd | Wholesale & retail | 2021 |
| JIN JIN Chinese Ltd | Hospitality | 2023 |
| Jing HE Limited | Wholesale & retail | 2019 |
| Jinn IP Limited | Professional & scientific | 2015 |
| Jitney Limited | Transport & logistics | 2024 |
| Jittu & Swapna Ltd | Health & social care | 2023 |
| JIU Jitsu Republic Ltd | Arts & recreation | 2021 |
| Jivala Ltd | Manufacturing | 2026 |
| JJ & Sterling Developments Ltd | Construction | 2025 |
| JJ Enterprises Abingdon Limited | Hospitality | 2018 |
| JJ Pandit Ltd | Professional & scientific | 2011 |
| JJ Property London Limited | Construction | 2026 |
| JJ West Build & Co Ltd | Financial services | 2025 |
| Jj&S Ventures Limited | Hospitality | 2026 |
| JJL (Witney) Limited | Real estate | 2017 |
| JJL Electrical Services Ltd | Construction | 2023 |
| JJS Automotive Ltd | Wholesale & retail | 2023 |
| JJS Minerals Co. Limited | Mining & quarrying | 2009 |
| JK Barbers Ltd | Other services | 2016 |
| JK LAU Properties Ltd | Real estate | 2024 |