| M Imran Ltd | Wholesale & retail | 2022 |
| M J Property Investment Holdings Ltd | Real estate | 2023 |
| M K H K Developments Limited | Construction | 2020 |
| M K Watts Ground Maintenance Limited | Administrative & support | 2010 |
| M Kerr Consulting Ltd | Professional & scientific | 2022 |
| M L Management Ltd | Households | 2017 |
| M M Drapes Limited | Information & communication | 2020 |
| M N Security Limited | Administrative & support | 2019 |
| M P G Legal Services Ltd | Professional & scientific | 2019 |
| M Plus Interior Limited | Construction | 2025 |
| M R Constructions Oxford Ltd | Construction | 2020 |
| M Salem Medical Services Limited | Health & social care | 2020 |
| M&A Handyman Ltd | Construction | 2026 |
| M&B Property Services Limited | Households | 2024 |
| M&F Dental Clinic Limited | Health & social care | 2011 |
| M&I DAR Ltd | Wholesale & retail | 2016 |
| M&Q Car Traders Ltd | Wholesale & retail | 2019 |
| M&S Chauffeurs Ltd | Transport & logistics | 2026 |
| M&S Oxford Ltd | Real estate | 2025 |
| M&S Property Maintenance and Cleaning Services Ltd | Other services | 2016 |
| M&X General Builders Ltd | Construction | 2025 |
| M. J. FEW Plumbing & Heating Limited | Construction | 2003 |
| M.A.R.E.S-Kendricks Inc Ltd | Health & social care | 2016 |
| M.C.Barr Ltd | Real estate | 2022 |
| M.D. Hamilton (Farms) Limited | Agriculture & fishing | 1993 |
| M.K. Dobson Property Limited | Real estate | 2026 |
| M.Kaur Ltd | Real estate | 2026 |
| M.Razaghi Consulting Ltd | Information & communication | 2016 |
| M3A Ltd | Wholesale & retail | 2025 |
| M4 Home Improvements Limited | Construction | 2013 |
| M4 Joinery Limited | Wholesale & retail | 2024 |
| MA & AB Investments Ltd | Real estate | 2019 |
| MA Wyatt Ltd | Construction | 2021 |
| Maaruti Technologies Ltd | Information & communication | 2011 |
| Maawu DA Company Ltd | Households | 2011 |
| Mablethorpe Hall Ltd | Real estate | 2023 |
| Mabsolve Limited | Professional & scientific | 2019 |
| MAC & DEE Limited | Administrative & support | 2011 |
| Macdonald UK Obstetric Medicine Society | Other services | 2012 |
| Mace Homes Limited | Construction | 2014 |
| MACH42 Limited | Professional & scientific | 2019 |
| Machine Shop Interiors & Design Limited | Manufacturing | 2019 |
| Machineforest Limited | Manufacturing | 2008 |
| Macjohn Consulting Ltd | Professional & scientific | 2006 |
| Mackenzie Facility Management Ltd | Administrative & support | 2025 |
| Macpherson Hospitality LLP | | 2023 |
| Madani Green Health Limited | Wholesale & retail | 2025 |
| Maddy Construction Limited | Construction | 2025 |
| Made (Oxford) Ltd | Professional & scientific | 2024 |
| Made by Meya Ltd | Other services | 2023 |
| Made Clear Studios Ltd | Other services | 2010 |
| Made of Good Ltd | Construction | 2023 |
| Madhuli Estate Assets LLP | | 2019 |
| Madni Technologies (UK) Limited | Arts & recreation | 2015 |
| Madronero Ltd | Health & social care | 2025 |
| Maeguemechs Limited | Manufacturing | 2019 |
| Magdalen Bridge Boathouse Limited | Arts & recreation | 2006 |
| Magdalen Builders Limited | Construction | 2023 |
| Magdalen College Educational Conferences Limited | Administrative & support | 2008 |
| Magdalen College School International Limited | Education | 2017 |
| Magdalen College School Oxford Limited | Education | 1987 |
| Magdalen College Trading Limited | Administrative & support | 2008 |
| Magdalen Development Company Limited | Construction | 1986 |
| Magdalen Road Church Development Ltd | Construction | 2017 |
| Magee Scientific (UK) Limited | Financial services | 2012 |
| Magellan Science Limited | Professional & scientific | 2019 |
| Magenta Insight Ltd | Professional & scientific | 2022 |
| Magi Consulting Limited | Professional & scientific | 2017 |
| Magic Travel Limited | Administrative & support | 2016 |
| Magicdeea Clean Ltd | Administrative & support | 2025 |
| Magnetic Impressions Ltd | Manufacturing | 2025 |
| Magnex Scientific Ltd | Professional & scientific | 2011 |
| Magnocarta Limited | Information & communication | 2014 |
| Magnus Warbouys Limited | Information & communication | 2010 |
| Maha Music Ltd | Education | 2025 |
| Mahal Logistics Ltd | Transport & logistics | 2025 |
| Maharaja Drinks Emporium Limited | Wholesale & retail | 2022 |
| Mahee Tandoori Ltd | Hospitality | 2015 |
| Mahmood 2025 Estates Limited | Real estate | 2025 |
| Mahogany Hair Limited | Other services | 2020 |
| Maiden Lane Development Management Company Limited | Real estate | 1986 |
| Maioriello Legal Services Limited | Professional & scientific | 2024 |
| Mairco Ltd | Professional & scientific | 2018 |
| Maison Lumiere Ltd. | Education | 2017 |
| Maison Maintenance Care Ltd | Construction | 2025 |
| Majestic Art Ltd | Wholesale & retail | 2024 |
| Majestic Insights Limited | Information & communication | 2022 |
| Make IT Count Consulting Ltd | Professional & scientific | 2026 |
| Make IT, Move IT Ltd | Education | 2018 |
| Make Space Oxford C.I.C. | Real estate | 2015 |
| Make Time for Music Limited | Education | 2004 |
| Makeover Beauty Salon Ltd | Other services | 2025 |
| Makmat Management Limited | Other services | 2009 |
| Malatang Oxford Ltd | Hospitality | 2024 |
| Malebon Aylesbury Ltd | Hospitality | 2018 |
| Malet Street Research Limited | Professional & scientific | 2026 |
| Malgil Ltd | Hospitality | 2015 |
| Malgrif Ltd | Real estate | 2023 |
| Mali B Ltd | Construction | 2026 |
| Malik's Homes Group Ltd | Real estate | 2025 |