| Isis Indemnity Scheme Ltd | Professional & scientific | 2010 |
| Isis Leasing Limited | Real estate | 1998 |
| Isis Residents Association Limited | Real estate | 2007 |
| Isis Sports Limited | Professional & scientific | 2014 |
| Isla Vita Ltd | Wholesale & retail | 2025 |
| Islamic Beginnings Ltd | Wholesale & retail | 2018 |
| Islington Green Limited | Professional & scientific | 2007 |
| Islip Consulting Limited | Financial services | 2004 |
| Islip Motors Limited | Wholesale & retail | 2008 |
| Islip Place Management Company Limited | Households | 2019 |
| Islip Road Management Company Limited | Households | 2007 |
| Isogenix Limited | Professional & scientific | 2022 |
| Isra Limited | Wholesale & retail | 2011 |
| Istanbul Barber 1995 Ltd | Other services | 2025 |
| IT Academy Oxford Ltd | Education | 2025 |
| IT Mavens Limited | Information & communication | 2011 |
| IT Must BE Green Limited | Wholesale & retail | 2007 |
| It's Time for Change Limited | Professional & scientific | 2026 |
| Italiamo Bellezza Ltd | Other services | 2024 |
| Italiamo Ltd | Hospitality | 2020 |
| Italiamo MS Deli Ltd | Hospitality | 2022 |
| Italiamo MS Ltd | Hospitality | 2023 |
| Italian Bites Ltd | Hospitality | 2019 |
| Itcality Ltd | Extraterritorial | 2019 |
| Item Club Limited | Information & communication | 1987 |
| Itext Limited | Information & communication | 1992 |
| Ithaka Properties Limited | Real estate | 2016 |
| ITL Design Ltd | Professional & scientific | 2022 |
| Itmattersuk Limited | Other services | 2022 |
| ITR Service Limited | Professional & scientific | 2008 |
| ITS Roop Ltd | Wholesale & retail | 2025 |
| IVE Sent IT Ltd | Information & communication | 2018 |
| Ivenso Investments Ltd | Real estate | 2019 |
| Iverna Properties Limited | Real estate | 2013 |
| IVI UK Ltd | Health & social care | 2015 |
| Ivor Johns & Sons | | 1995 |
| Ivor Terrill Auto Electrical Limited | Wholesale & retail | 2002 |
| IVY Maraney Limited | Wholesale & retail | 2021 |
| Ivyrose Ltd | Information & communication | 2003 |
| J & H Lynch Limited | Construction | 2021 |
| J & M Janecek (Oxford) Limited | Real estate | 1960 |
| J & P Roper Limited | Construction | 2006 |
| J & R Farming Ltd | Agriculture & fishing | 2020 |
| J B Electrical (Oxford) Ltd | Construction | 2005 |
| J C J Builders Ltd | Construction | 2025 |
| J D S (Oxford) Limited | Professional & scientific | 1994 |
| J E B R I Limited | Administrative & support | 2009 |
| J M Florey Properties Ltd | Real estate | 2025 |
| J P Cabinetry Ltd | Manufacturing | 2020 |
| J P Horsington Limited | Information & communication | 2026 |
| J Ridout Building Services Limited | Construction | 2013 |
| J S Mitchell Limited | Professional & scientific | 2012 |
| J&B Bulk Haulage Limited | Wholesale & retail | 1998 |
| J&B Cars Limited | Transport & logistics | 2013 |
| J&B Group Holdings Limited | Financial services | 2023 |
| J&B Oxford Ltd | Real estate | 2022 |
| J&C Management Consultants Limited | Professional & scientific | 2018 |
| J&D Automotive Ltd | Wholesale & retail | 2026 |
| J&D Oxford Ltd | Hospitality | 2025 |
| J&J AM Hospitality Limited | Hospitality | 2024 |
| J&L Property (Oxford) Limited | Real estate | 2019 |
| J&N Mini Marvels Ltd | Wholesale & retail | 2025 |
| J&P Clean Oxford Limited | Administrative & support | 2024 |
| J'S Sports Bar Ltd | Hospitality | 2017 |
| J. & P. Hedges (Farmers) Limited | Agriculture & fishing | 1964 |
| J. Barney (Plant Hire) Limited | | 1973 |
| J.A. Pearce Engineering Limited | Construction | 2017 |
| J.Brand Limited | Construction | 1933 |
| J.E. Pill & Sons Ltd | Manufacturing | 2008 |
| J.P. Harvey Ltd | Financial services | 2026 |
| J.R. Baughan Limited | Construction | 1994 |
| J.W.I Electrical Limited | Construction | 2016 |
| J3DI Engineering Ltd | Professional & scientific | 2022 |
| JA1 Transport Limited | Transport & logistics | 2019 |
| Jachar Ltd | Health & social care | 2013 |
| Jackel & Mitchell Ltd | Information & communication | 2019 |
| Jacobsassets Ltd | Information & communication | 2025 |
| Jahlso Limited | Real estate | 2021 |
| Jake & Barney Limited | Arts & recreation | 2017 |
| Jakeman Consulting Ltd | Education | 2021 |
| Jakz Rigging Servcices Ltd | Construction | 2026 |
| Jaldi Limited | Professional & scientific | 2013 |
| Jamals Indian Ltd | Hospitality | 2026 |
| James Bloor Limited | Wholesale & retail | 2000 |
| James C Penny (Estate Agents) Limited | Real estate | 2009 |
| James C Penny (Lettings) Limited | Real estate | 2009 |
| James Donoghue (Plastering Contractors) Limited | Construction | 2013 |
| James Forder Economics Limited | Professional & scientific | 2010 |
| James House Management (Oxford) Limited | Households | 1993 |
| James Mortimer Studio Limited | Arts & recreation | 2019 |
| James Nicholson Ltd | Extraterritorial | 2023 |
| James Ramus General Surgery Limited | Health & social care | 2012 |
| James Turnock Bespoke Ltd | Construction | 2025 |
| James Wyman Architects Ltd | Professional & scientific | 2014 |
| Jamesmforshaw Ltd | Health & social care | 2023 |
| Jamestech Solutions Ltd | Information & communication | 2026 |
| Jamjar Creative Limited | Professional & scientific | 2008 |
| Jamona (UK) Ltd | Hospitality | 2018 |
| Jane & MAY Ltd | Wholesale & retail | 2025 |
| Jane Rowe Consulting Limited | Professional & scientific | 2016 |