| MCP Multimedia Ltd | Information & communication | 2017 |
| MCP Wealth Management Limited | Financial services | 2018 |
| MDC Nominees Limited | Professional & scientific | 2015 |
| MDL Property Ltd | Real estate | 2025 |
| MDS Property Management Ltd | Real estate | 2021 |
| ME and My Retail Limited | Wholesale & retail | 2012 |
| Meadow Court Witney Limited | Real estate | 2023 |
| Meadow Hill Properties Limited | Real estate | 1963 |
| Meadows Abbey Farm Limited | Financial services | 2025 |
| Meckel Limited | Construction | 2017 |
| Medaxistalent Ltd | Administrative & support | 2026 |
| Medfolio Ltd | Information & communication | 2024 |
| Mediation Inspires Limited | Professional & scientific | 2009 |
| Medileve Limited | Health & social care | 1998 |
| Meditraining Ltd | Health & social care | 2020 |
| Meech Air Technology Limited | Professional & scientific | 1995 |
| Meech Static Eliminators (USA) Limited | Professional & scientific | 1992 |
| Meech Static Eliminators Limited | Manufacturing | 1980 |
| Mehis Capital Ltd | Financial services | 2026 |
| Mehis Group Limited | Real estate | 2022 |
| Meica Technical Services (MTS) Ltd | Construction | 2016 |
| Menssana Martial Arts Ltd | Education | 2022 |
| Mercer Gardens Management Limited | Households | 2019 |
| Merlin IT Limited | Information & communication | 1997 |
| Merlin Marketing and IT Ltd | Information & communication | 2017 |
| Merlin XL Limited | Information & communication | 2007 |
| Merlinxl Investments Limited | Financial services | 2021 |
| Metaship Limited | Information & communication | 2025 |
| Metaxis Limited | Information & communication | 2007 |
| Metis Cyber Consulting Ltd | Administrative & support | 2014 |
| Metisse Engines Limited | Professional & scientific | 2016 |
| Metisse Motor Cycles Limited | Wholesale & retail | 1999 |
| MF Advisory Limited | Professional & scientific | 2025 |
| MFD Partners International Limited | Professional & scientific | 2008 |
| MFR (UK) Limited | Administrative & support | 2007 |
| MG Graphics Limited | Professional & scientific | 2011 |
| MG House Management Company Limited | Households | 2007 |
| MG Properties (Oxford) Ltd | Real estate | 2018 |
| MG Trucker Ltd | Wholesale & retail | 2016 |
| MGI Aerospace Ltd | Professional & scientific | 2022 |
| MGI Engineering Ltd | Professional & scientific | 2003 |
| MH Car Sales Oxford Limited | Wholesale & retail | 2013 |
| Mhcfhealth Ltd | Health & social care | 2023 |
| MHJ IT Services Ltd | Information & communication | 2014 |
| MHW (Oxon) Ltd | Construction | 2013 |
| Mica Property Ltd | Real estate | 2022 |
| Michael Skipwith Limited | Health & social care | 2009 |
| Micjon Ltd | Construction | 2016 |
| Mick's Skips Limited | Administrative & support | 2003 |
| Micro Holdings Group Ltd | Administrative & support | 2011 |
| Micro Technology Systems Ltd | Professional & scientific | 2000 |
| MICRO2ME Limited | Administrative & support | 2018 |
| Micromagnetics Limited | Administrative & support | 2018 |
| Micromarketing Limited | Wholesale & retail | 2005 |
| Middleton Project Consultancy Ltd | Information & communication | 2025 |
| Mighty Oak Training Ltd | Education | 2021 |
| Miinor Studios Ltd | Other services | 2026 |
| Mike Gilbert Planning Ltd | Professional & scientific | 2013 |
| Mike Sinfield Limited | Professional & scientific | 2012 |
| Milava Holdings Limited | Financial services | 2026 |
| Milava Limited | Financial services | 2016 |
| Milena Windows Limited | Wholesale & retail | 2004 |
| Miles Plant Limited | Real estate | 1988 |
| Mill Street Arts Ltd | Education | 2023 |
| Mill Street Management Number 1 Limited | Real estate | 2010 |
| Millfield Contractors Ltd | Construction | 2012 |
| Millhouse Construction Limited | Construction | 2008 |
| Millie FOX Limited | Wholesale & retail | 2004 |
| Millins Yard Freehold Limited | Administrative & support | 2025 |
| Millstream (Spare) Ltd | Other services | 2026 |
| Millstream Mews Witney Ltd | Other services | 2026 |
| Millszac Ltd | Financial services | 2019 |
| Millwood Market Garden Ltd | Agriculture & fishing | 2016 |
| Milne Builders Limited | Construction | 1979 |
| Milner and Nocetti-Haworth Ltd | Other services | 2022 |
| Minchinvest Limited | Financial services | 2026 |
| Mind & Muscle (Witney) Limited | Arts & recreation | 2025 |
| Mind Alchemy Ltd | Other services | 2023 |
| Mindful Care Oxon Limited | Health & social care | 2025 |
| Minster Joinery (Witney) Limited | Manufacturing | 2011 |
| Minster Lovell Contracting Group Ltd | Construction | 2024 |
| Minster Lovell Contractors Limited | Construction | 1984 |
| Minster Lovell Homes Limited | Construction | 2025 |
| Minster Lovell Management Company Limited | Households | 2016 |
| Mirza Spice Ltd | Hospitality | 2025 |
| Mission Fitness UK Gym Ltd | Arts & recreation | 2024 |
| Mission NET Zero (2050) Ltd | Professional & scientific | 2026 |
| Missions That Matter Limited | Professional & scientific | 2017 |
| Misson Medical Services Ltd | Health & social care | 2012 |
| Mistry Cleaners Ltd | Other services | 2011 |
| Mitchell Anderson Limited | Administrative & support | 2007 |
| MIX of Nations Ltd | Information & communication | 2021 |
| MJ and EJ Cook Limited | Real estate | 2012 |
| MJC Construction & Home Improvements Limited | Construction | 2021 |
| MJC Total Electric Limited | Construction | 2025 |
| MJF & CLF Properties Ltd | Real estate | 2021 |
| MJY Carpentry Limited | Manufacturing | 2023 |
| MK Cardia Ltd | Health & social care | 2019 |
| MLC Building Services (Oxford) Limited | Construction | 2024 |
| MLJ Roofing Limited | Construction | 2021 |