| M. Naskali Oy | Real estate | 2020 |
| M. Pihl Oy | Construction | 2007 |
| Maanrakennus P.J Mäkelä OY | Construction | 2008 |
| MAITI Oy | Hospitality | 2016 |
| MAIU Sushi and Japanese dining Oy | Hospitality | 2015 |
| Marverk OY | Construction | 2012 |
| Maser OY | Financial services | 1987 |
| Master Sport OY | Wholesale & retail | 2012 |
| MB Pori Ky | Wholesale & retail | 1986 |
| MCW Group Oy | Professional & scientific | 2022 |
| MCW Laakkonen Oy | Manufacturing | 2016 |
| Meri-Porin Rakennus OY | Construction | 2002 |
| Meribor Ky | Construction | 2013 |
| MG Offshore Oy | Professional & scientific | 2025 |
| MHM Group Oy | Construction | 2023 |
| MHR Yhtiöt Oy | Construction | 2019 |
| Miperi OY | Administrative & support | 2018 |
| Mixonix OY | Hospitality | 2006 |
| MJA Tekniikka Oy | Real estate | 2025 |
| MJH-Pinnoitus Ky | Construction | 2017 |
| MJT Toimistopalvelut Oy | Real estate | 2014 |
| MK Consulting Group Oy | Professional & scientific | 2019 |
| MK Perämäki Oy | Wholesale & retail | 1972 |
| MK Suominen Oy | Real estate | 2014 |
| MKS Turku Holding Oy | Real estate | 2020 |
| MKV-Kiinteistöt Oy | Real estate | 2016 |
| ML-Melos Ky | Wholesale & retail | 2014 |
| MM Homes & Premises Oy | Real estate | 2012 |
| MM Housing Oy | Real estate | 2015 |
| Monting P.S.D.O.O. Za Izgradn, U Objekata, Suomen Sivuliike | Construction | 2008 |
| MOjala Invest Oy | Real estate | 2021 |
| MPJ Works Oy | Construction | 2025 |
| MS Auto Oy | Other services | 2025 |
| MS Tuotantopalvelut Oy | Arts & recreation | 2022 |
| MT Maritime Oy | Financial services | 2018 |
| MT Pelti- ja Eristys Oy | Construction | 2024 |
| MT-Plastics Oy | Wholesale & retail | 1993 |
| Muuraus / Laatoitus Osju OY | Construction | 2007 |
| MVR Invest Oy | Real estate | 2007 |
| MVR-Yhtymä Oy | Construction | 2007 |
| MY-Consulting Ky | Professional & scientific | 2017 |
| Ma-Tina Oy | Manufacturing | 2016 |
| MaSa Rakennukset Oy | Wholesale & retail | 2024 |
| Maa- ja rakennustekniikka MAK Oy | Construction | 2020 |
| Maa-Invest Ky | Real estate | 1976 |
| Maalaamo P. Aaltonen Oy | Administrative & support | 1980 |
| Maalaus Rantamäki Oy | Construction | 2017 |
| Maalaus ja saneeraus 100 Oy | Construction | 2024 |
| Maalaus-AMI Oy | Construction | 2010 |
| Maalaus-Faakeri Ky | Construction | 1966 |
| Maalausliike AR Oy | Construction | 2012 |
| Maalausliike Tuomikoski Oy | Construction | 1992 |
| Maanrakennus Esa Virtanen Ky | Construction | 2008 |
| Maanrakennus Mäenpää Oy | Construction | 1987 |
| Maanrakennus Pasi Virtanen Ky | Transport & logistics | 2006 |
| Maanrakennus T Viljanen Oy | Construction | 2012 |
| Maanrakennus Tero Elo Oy | Construction | 2019 |
| Maarit Järvinen Oy | Hospitality | 1999 |
| Maatalouden tilitoimisto, agronomi Matti Jokinen, avoin yhtiö | Information & communication | 2009 |
| Macecraft Oy | Information & communication | 2002 |
| Mad Fellows Service Oy | Other services | 2018 |
| Madam Heikkinen Ky | Hospitality | 1986 |
| Mai Ines oy | Other services | 2017 |
| Mainos Ottilia Oy | Wholesale & retail | 2000 |
| Mainoskuvaamo Esa Kyyrö Ky | Professional & scientific | 1980 |
| Mainosmasiina Oy | Professional & scientific | 2014 |
| Mainospalvelu Ruohonen, Kommandiittiyhtiö | Professional & scientific | 1977 |
| Mainosruutu Oy | Professional & scientific | 1993 |
| Mainosvarjus Oy | Professional & scientific | 1995 |
| Maisemasauna Amado Oy | Real estate | 1998 |
| Maisemassa Oy | Professional & scientific | 2024 |
| Majakas Holding Oy | Real estate | 2021 |
| Makera Oy | Construction | 2025 |
| Makpe Oy | Wholesale & retail | 2022 |
| Makwana Moppers Oy | Administrative & support | 2024 |
| Malimet Oy | Wholesale & retail | 2022 |
| Mallitoimisto Ami Ky | Professional & scientific | 1986 |
| Manetec Ky | Professional & scientific | 2017 |
| Maniac Mani Oy | Other services | 2026 |
| Mannerlaukku Ky | Wholesale & retail | 2008 |
| Manninen HSEQ -Palvelut Oy | Professional & scientific | 2025 |
| Manu Toivonen Consulting Kommandiittiyhtiö | Professional & scientific | 1985 |
| Manu Toivonen Training Company Oy | Education | 1998 |
| Manweld Oy | Wholesale & retail | 1990 |
| Marika Vitikkala Oy | Health & social care | 2020 |
| Marina Merilokki Oy | Transport & logistics | 1999 |
| Marium Oy | Transport & logistics | 2022 |
| Marjanen & Kni Oy | Financial services | 2002 |
| Markku Hahto Oy | Wholesale & retail | 1992 |
| Markku Pajuniemi Oy | Financial services | 1985 |
| Marsaki Oy | Construction | 1987 |
| Marsiran Oy | Financial services | 1987 |
| Marvaco Oy | Manufacturing | 2008 |
| MaseCon Oy | Construction | 2021 |
| Maso Oy | Real estate | 2017 |
| Matalakari Oy | Real estate | 2016 |
| Matavi Services Oy | Professional & scientific | 2019 |
| Matkatoimisto Matkapassi Ky | Administrative & support | 1983 |
| Matte Invest Oy | Wholesale & retail | 2007 |
| Matti Jakonen Oy | Real estate | 1983 |