| North Point Electrical Ltd | Construction | 2018 |
| North Star Research Limited | Professional & scientific | 2022 |
| North Street Associates Limited | Professional & scientific | 2017 |
| North Street Consultants Limited | Professional & scientific | 2018 |
| Northampton Professional Valeting Services Ltd | Administrative & support | 2018 |
| Northbrook Systems Ltd | Other services | 2025 |
| Northfield Property Group Ltd | Real estate | 2026 |
| Northledger Accounting Ltd | Professional & scientific | 2026 |
| Northmanor Limited | Hospitality | 2000 |
| Northmoor Limited | Extraterritorial | 2024 |
| Northport BIO Ltd | Professional & scientific | 2024 |
| Northsky Property Investment Ltd | Real estate | 2026 |
| Northway Pizza Limited | Hospitality | 2023 |
| Northway Together CIC | Education | 2022 |
| NOS Investment Limited | Real estate | 2021 |
| Nosht Limited | Information & communication | 2026 |
| Nostalgia Travel Limited | Other services | 1946 |
| Notion Neuroimaging Ltd | Health & social care | 2024 |
| Nouman Ijaz Ltd | Wholesale & retail | 2025 |
| Nourish Yoga Training Limited | Other services | 2017 |
| Nova Living Property Managemet Ltd | Real estate | 2025 |
| Nova Nannies Limited | Education | 2025 |
| Novadata Solutions Ltd | Information & communication | 2017 |
| Novage Academy Ltd | Education | 2016 |
| Novaluxe Jewellery Ltd | Wholesale & retail | 2025 |
| Novandi Limited | Professional & scientific | 2016 |
| Novasmart Ltd | Information & communication | 2015 |
| Novello Properties Limited | Real estate | 1985 |
| Novit Ltd | Information & communication | 2017 |
| Novo Nordisk Research and Development UK Limited | Professional & scientific | 2014 |
| Novogen Labs Ltd | Wholesale & retail | 2023 |
| Novus Insights Limited | Information & communication | 2023 |
| Novus Space Limited | Professional & scientific | 2018 |
| NRM Oxford Ltd | Hospitality | 2021 |
| NRT Joinery Limited | Construction | 2013 |
| NS Properties Oxford Ltd | Real estate | 2024 |
| NSF Certification UK Limited | Other services | 1997 |
| NSF International UK Limited | Financial services | 2007 |
| NSF Safety and Quality UK Limited | Other services | 1985 |
| Ntrs (Oxford) Ltd | Other services | 2022 |
| Nttau Digital Ltd | Professional & scientific | 2022 |
| Nuclear Careers Ltd | Administrative & support | 2025 |
| Nucleome Therapeutics Limited | Professional & scientific | 2019 |
| Nucleus Educate Ltd | Education | 2026 |
| Nuffield College Developments 1 Limited | Construction | 2016 |
| Nuffield Court Management Company Limited | Households | 1998 |
| Nuffield Critical Care LLP | | 2017 |
| Nuffield Garage Limited | Wholesale & retail | 2006 |
| Number Sense Maths Limited | Administrative & support | 2017 |
| Numerical Algorithms Group Limited (the) | Information & communication | 1976 |
| Numericanalysis Ltd | Professional & scientific | 2010 |
| Numerico Limited | Extraterritorial | 2019 |
| Numicon Limited | Information & communication | 1998 |
| Nuneham Courtenay Glebe Limited | Professional & scientific | 2005 |
| Nurture and Bloom Psychology Ltd | Education | 2025 |
| Nurture Fertility Limited | Health & social care | 2016 |
| NV Estates Limited | Real estate | 2015 |
| Nvisiq Ltd | Professional & scientific | 2024 |
| NWB Oxford Education Consultancy Ltd | Education | 2014 |
| NXT LVL Aesthetics Limited | Health & social care | 2024 |
| Nylon Colours Trustees Limited | Financial services | 2024 |
| NYM Services Limited | Health & social care | 2024 |
| Nyng Ltd | Administrative & support | 2026 |
| O&A Property Maintenance Ltd | Construction | 2016 |
| O'Brien (Oxford) Limited | Financial services | 2006 |
| O'Brien Building Services Limited | Construction | 2014 |
| O'Brien Interiors Limited | Construction | 2004 |
| O'Clean Services Ltd | Administrative & support | 2022 |
| O'Dowda-Boswell Ltd | Professional & scientific | 2025 |
| O.F.D.Education Limited | Education | 2017 |
| OA Consulting Limited | Information & communication | 2010 |
| OAI Ltd | Information & communication | 2025 |
| Oak & Stone Constructors Limited | Construction | 2025 |
| Oak Build JD Ltd | Construction | 2023 |
| Oakcircle Limited | Real estate | 1983 |
| Oakeshott Society Limited | Other services | 2023 |
| Oakley Court Management Company Limited | Households | 2001 |
| Oakmont Limited | Information & communication | 1996 |
| Oakthorpe Consulting Limited | Financial services | 2021 |
| Oakthorpe Holdings Limited | Financial services | 2026 |
| Oakthorpe Practices Limited | Health & social care | 2012 |
| OBC Fintech Limited | Information & communication | 2022 |
| Obelis UK Ltd | Professional & scientific | 2018 |
| Obergine Limited | Information & communication | 2006 |
| Oberix Group Ltd | Professional & scientific | 2012 |
| Obeya Holdings Ltd | Extraterritorial | 2018 |
| Objects of USE Ltd | Wholesale & retail | 2022 |
| Obo&Lasisi Consultancy Ltd | Hospitality | 2026 |
| Obsaint Care Ltd | Health & social care | 2021 |
| Obsidian Research Ltd | Education | 2019 |
| Obsidian Surgical Ltd | Health & social care | 2024 |
| Obtainium Venture Technicalists Ltd | Professional & scientific | 2024 |
| Ocakbasi Ltd | Hospitality | 2024 |
| OCB Insights Limited | Professional & scientific | 2022 |
| Occa House Limited | Education | 1997 |
| OCD Cleaning Ltd | Administrative & support | 2025 |
| Ocean Innovation Solutions Ltd | Administrative & support | 2011 |
| Ocean of Wisdom Publishing C.I.C. | Information & communication | 2025 |
| Ocean Revive (UK) Ltd | Professional & scientific | 2022 |
| Ocean Wave Engineering Limited | Professional & scientific | 1999 |