| Mansen Levytyö Oy | Manufacturing | 1984 |
| Mansen Maalarit Oy | Construction | 2022 |
| Mansen Makkarat Ky | Hospitality | 2019 |
| Mansen PR-Huolto Oy | Wholesale & retail | 1999 |
| Mansen Pohjarakenne Oy | Construction | 2016 |
| Mansen Suutari Oy | Other services | 2007 |
| Mansen Tennis Oy | Real estate | 1983 |
| Mansen Tikki Ky | Wholesale & retail | 1987 |
| Mansen infrapalvelut Ky | Transport & logistics | 2013 |
| Mansen vihannes Oy | Wholesale & retail | 1981 |
| Mansepori Oy | Wholesale & retail | 2000 |
| Manserock Oy | Information & communication | 1992 |
| Mansetech Oy | Information & communication | 2012 |
| Mansoniemi Transport Oy | Transport & logistics | 2022 |
| Mansutec Oy | Manufacturing | 2020 |
| Mantara Oy | Administrative & support | 2024 |
| Manyone Oy | Education | 2015 |
| Maper Oy | Manufacturing | 2022 |
| MarMan Oy | Real estate | 2021 |
| MarPel Dent Oy | Health & social care | 1997 |
| Maran AG Oy | Hospitality | 2026 |
| Maravita Oy | Construction | 2015 |
| Marco Äijälä Oy | Professional & scientific | 2015 |
| MariMind Oy | Health & social care | 2025 |
| Maria Aitomaa Oy | Education | 2020 |
| Maria ja Jukka Säilä Oy | Wholesale & retail | 2016 |
| Marian Kotihoito Oy | Health & social care | 2026 |
| Mariankadun Rohdos Oy | Wholesale & retail | 2004 |
| Marie & Johannes Oy | Professional & scientific | 2020 |
| Marijo Partners Oy | Wholesale & retail | 2019 |
| Mariposa Ky | Wholesale & retail | 1989 |
| Marisse Oy | Transport & logistics | 2013 |
| Marizza Oy | Wholesale & retail | 2015 |
| Marja & Ester Oy | Arts & recreation | 2024 |
| Marjanella Oy | Financial services | 1976 |
| Marjataikurit Oy | Wholesale & retail | 2025 |
| Marjusani Oy | Real estate | 1994 |
| MarkQ Oy | Wholesale & retail | 2026 |
| Markab Oy | Professional & scientific | 2002 |
| Markan Paja Oy | Administrative & support | 2026 |
| Marketing Desk Oy | Information & communication | 2013 |
| Markka Consulting Oy | Professional & scientific | 2025 |
| Markkinointi ALT Oy | Wholesale & retail | 1994 |
| Markkinointi Halftime Oy | Professional & scientific | 1986 |
| Markkinointi Jari Nieminen Oy | Wholesale & retail | 1992 |
| Markkinointi Sillanaukee Oy | Financial services | 2012 |
| Markkinointi T.E.S.A. Oy | Manufacturing | 1989 |
| Markkinointitoimisto Deeper Oy | Professional & scientific | 2009 |
| Markkinointitoimisto Expression Oy | Professional & scientific | 2005 |
| Markkinointitoimisto Kyllä Onnistuu Oy | Professional & scientific | 2015 |
| Markkinointitoimisto Treil Oy | Professional & scientific | 2019 |
| Markkinointiviestinnän suunnittelutoimisto Mainio Oy | Professional & scientific | 2004 |
| Markkinointiviestintä Atomi Oy | Professional & scientific | 1998 |
| Markku Hakkarainen Ky | Construction | 1990 |
| Markku Okkonen Capital Oy | Health & social care | 2009 |
| Markku ja Minna Mäkisalo Oy | Manufacturing | 2016 |
| Marko Laaksonen Oy | Wholesale & retail | 2010 |
| Marko Manu Consulting Oy | Professional & scientific | 2020 |
| Marko Mulari Ky | Transport & logistics | 2012 |
| Marko Piispa Rakennuspalvelu Oy | Construction | 2017 |
| Marko Strand Oy | Wholesale & retail | 1998 |
| Markus Sinijärvi Oy | Construction | 2009 |
| Marlemi Oy | Manufacturing | 1976 |
| Marlind Oy | Financial services | 2025 |
| Marlion Oy | Financial services | 2024 |
| Marmacon Oy | Professional & scientific | 1989 |
| Marpaco Oy | Financial services | 2021 |
| Marshfield Oy | Information & communication | 2017 |
| Martti Määttä Osakeyhtiö | Construction | 2013 |
| Marttilan Pirtti Oy | Hospitality | 1996 |
| Marvea Kodit Oy | Real estate | 2020 |
| Marvea Kymppikodit Oy | Real estate | 2024 |
| Marvea Oy | Construction | 2019 |
| Marvea Pirkanmaa Oy | Construction | 2025 |
| MasaMainio Oy | Real estate | 2024 |
| MasaTapani Oy | Construction | 2023 |
| Masahiro Oy | Financial services | 2024 |
| Masihouse Oy | Real estate | 2019 |
| Masion Oy | Real estate | 2013 |
| Masor Electrics Oy | Construction | 2016 |
| Massquad Oy | Professional & scientific | 2018 |
| Master Dent Oy | Manufacturing | 2023 |
| Master English Oy | Education | 2009 |
| Master Mind Intelligence Oy | Information & communication | 2025 |
| Master-K Oy Solution | Professional & scientific | 2009 |
| Masterbar Oy | Hospitality | 2020 |
| Mastermade Oy | Hospitality | 2017 |
| Masterpiece Interior Design Oy | Professional & scientific | 2026 |
| Mastik Oy | Professional & scientific | 2024 |
| Mastonkulman Kirja- ja Paperikauppa Ky | Wholesale & retail | 1992 |
| Masu invest Oy | Financial services | 2026 |
| Matecon Oy | Professional & scientific | 1984 |
| Material Factor Oy | Professional & scientific | 2022 |
| Math NetSupport Finland Oy | Education | 2012 |
| Matias Rimmi Oy | Wholesale & retail | 2021 |
| Matinco Oy | Real estate | 1989 |
| Matinlahden Maanrakennus Oy | Construction | 1990 |
| Matinlahden Toimitilat Oy | Construction | 1996 |
| Matka- ja Nahkatavaraliike Suhonen Oy | Wholesale & retail | 1977 |
| Matka-Tavastia Oy | Administrative & support | 1989 |