| Inspired Engineering Design Limited | Manufacturing | 2003 |
| Inspired Minds UK Consulting Ltd | Extraterritorial | 2024 |
| Inspired Wealth Solutions Limited | Professional & scientific | 2009 |
| Integra IP Limited | Administrative & support | 2010 |
| International Patient Experience Academy Ltd | Education | 2023 |
| Intertronics Holdings Ltd | Financial services | 2023 |
| Interzone Music Publishing Limited | Arts & recreation | 1996 |
| Introtrain & Forum Limited | Education | 2001 |
| Invoice 24 Limited | Information & communication | 2024 |
| IP Asset LLP | | 2005 |
| IP Seccurtv Ltd | Information & communication | 2011 |
| IPM Accessories Ltd | Wholesale & retail | 2020 |
| IQ Insurance Services Limited | Financial services | 2002 |
| Islip Village Hall Limited | Professional & scientific | 2004 |
| Islip Village Shop Limited | Wholesale & retail | 2004 |
| Isogonic Limited | Information & communication | 2003 |
| It-Izydorek Ltd | Administrative & support | 2024 |
| IVM Realty Limited | Real estate | 2025 |
| Izem Homes Ltd | Real estate | 2026 |
| J Burns Consultancy Ltd | Professional & scientific | 2026 |
| J D Print Solutions Limited | Manufacturing | 2017 |
| J Fenton and Co Limited | Real estate | 2022 |
| J MAC Education Ltd | Education | 2025 |
| J T Fasteners Limited | Wholesale & retail | 2003 |
| J&U Kini Private Limited | Health & social care | 2022 |
| J-Pw (Oxford) Ltd | Professional & scientific | 2018 |
| J.D.Lyne Ltd | Other services | 2024 |
| J.F.& P.A.Mcewen Limited | Hospitality | 1957 |
| J2 Electrical Services Limited | Construction | 2022 |
| Jack Knight Ltd | Manufacturing | 2023 |
| Jack Rabbit Vapes Ltd | Manufacturing | 2016 |
| Jak's Barbers Ltd | Other services | 2023 |
| JAM Property Investments Limited | Real estate | 2018 |
| Jamil K Ltd | Health & social care | 2015 |
| Jarda Consulting Ltd | Information & communication | 2019 |
| JCS Holdings (Oxford) Ltd | Financial services | 2026 |
| JDT Construction Ltd | Construction | 2019 |
| Jebster Limited | Real estate | 2023 |
| Jerrams Brothers Funeral Directors Limited | Other services | 2013 |
| JGF Building Services Ltd | Construction | 2020 |
| Jigsaw Security Solutions Limited | Construction | 2004 |
| JIM Boyland Trading Ltd | Administrative & support | 2011 |
| JJ Engineering Ltd | Professional & scientific | 2023 |
| JK Ductwork Services Ltd | Manufacturing | 2022 |
| JKG Independent Services Ltd | Wholesale & retail | 2019 |
| Jkrx Care Ltd | Health & social care | 2026 |
| JL Capital Holdings Ltd | Financial services | 2026 |
| JMC Holdings (Oxford) Limited | Financial services | 2020 |
| JMI - JET Maintenance International Ltd | Manufacturing | 2018 |
| JMI - JET Management International Ltd | Administrative & support | 2018 |
| JO Bagnall Ltd | Agriculture & fishing | 2010 |
| JO Wright Creative Ltd | Information & communication | 2023 |
| Joaben Ltd | Professional & scientific | 2017 |
| John David Frederick Stuart Limited | Extraterritorial | 2024 |
| John Finlay Ltd | Other services | 2012 |
| John Sheehan (Oxford) Limited | Construction | 1988 |
| Josh Florey Ltd | Construction | 2025 |
| Joy Community Care Limited | Health & social care | 2025 |
| Joy Music Ltd | Education | 2021 |
| JR Innovations Ltd | Administrative & support | 2025 |
| JS Motors Oxford Ltd | Wholesale & retail | 2012 |
| JSH Business Consultancy Limited | Professional & scientific | 2022 |
| JSJ Medica Ltd | Health & social care | 2024 |
| JT Madge Services Ltd | Other services | 2015 |
| JTP International (UK) LLP | | 2021 |
| JTS Homes Ltd | Construction | 2025 |
| Junction 6 Holdings Limited | Financial services | 2024 |
| Junction 6 Limited | Real estate | 2024 |
| Junction 6 Rugby Club Limited | Real estate | 2024 |
| Junction 6 Subco 2 Limited | Extraterritorial | 2024 |
| Junction 6 Subco 3 Limited | Extraterritorial | 2024 |
| Junction 6 Subco 4 Limited | Extraterritorial | 2024 |
| Junction 6 Subco 5 Limited | Extraterritorial | 2024 |
| Junction 6 Subco 6 Limited | Extraterritorial | 2024 |
| Junction 6 Subco 7 Limited | Extraterritorial | 2024 |
| Junction 6 Subco 8 Limited | Extraterritorial | 2024 |
| Just Cartridges Limited | Wholesale & retail | 2005 |
| Just GAS Heating Limited | Construction | 2014 |
| JWO Events Ltd | Wholesale & retail | 2024 |
| JWO Trade Limited | Wholesale & retail | 2025 |
| K.M.C Scaffolding Ltd | Construction | 2006 |
| Kaffirost Ltd | Wholesale & retail | 2024 |
| Kairos (Marlow) Limited | Information & communication | 2016 |
| Kajme Property Ltd | Real estate | 2025 |
| Karline Consultancy Ltd | Wholesale & retail | 2025 |
| Kaur Capital Group Ltd | Financial services | 2026 |
| Kayc Limited | Construction | 2018 |
| Kaysmet Limited | Construction | 2014 |
| KBS Wood Limited | Wholesale & retail | 2016 |
| Keble Homes Limited | Construction | 2003 |
| Keen and Keen Limited | Financial services | 2022 |
| Keen Limited | Wholesale & retail | 2001 |
| Keith Murray Consultants Limited | Real estate | 2010 |
| Kelburne Road Management Limited | Households | 2007 |
| Kendall Crescent Residents Company Limited | Real estate | 2004 |
| Kennington Flooring Limited | Construction | 2003 |
| KG Consulting Limited | Professional & scientific | 2024 |
| KGB Property Maintenance Services Ltd | Households | 2022 |
| Khaana Ltd | Hospitality | 2021 |
| Khandaan Properties Ltd | Real estate | 2025 |