| Munkkiniemen Remonttiapu Oy | Construction | 2005 |
| Munkkiniemen Suutari Oy | Other services | 2019 |
| Munkkiniemen Tennisklubi Oy | Arts & recreation | 2020 |
| Munkkiniemen pizzeria Oy | Hospitality | 2015 |
| Munkkiniemen rakennus ja saneeraus Oy | Construction | 2024 |
| Munkkiniemen yhteiskoulun kannatusosakeyhtiö | Real estate | 1949 |
| Munkkisaaren Floxet Oy | Professional & scientific | 2013 |
| Munkkisaaren peltityö Oy | Construction | 2008 |
| Munkkivuoren Kulma Oy | Wholesale & retail | 2022 |
| Munkkivuoren Puutarhakeidas Oy | Wholesale & retail | 2018 |
| Munkkivuoren Suutari Oy | Other services | 1994 |
| Muntilan Tuulivoima Oy | Energy | 2013 |
| Muntra Oy | Wholesale & retail | 2016 |
| Muohta Holding Oy | Financial services | 2023 |
| Muona Helsinki Oy | Hospitality | 2018 |
| Muonanrova Oy | Professional & scientific | 2021 |
| Muori & Pukki Official Oy | Arts & recreation | 2019 |
| Muoti Hovén Oy | Wholesale & retail | 1995 |
| Muoti-Susanne Ky | Wholesale & retail | 1985 |
| Muoti-Viiri Oy | Wholesale & retail | 1988 |
| Muotihuone Sariselavi Oy | Professional & scientific | 2008 |
| Muotiteltta Oy | Wholesale & retail | 2015 |
| Muotitorppa Oy | Wholesale & retail | 2008 |
| Muotitukka Oy | Other services | 1979 |
| Muotobetoni Oy | Professional & scientific | 2019 |
| Muotoiluosakeyhtiö Rönn | Professional & scientific | 2012 |
| Muotoiluosuuskunta Unionin26 | Arts & recreation | 1998 |
| Muotoilutoimisto Hartikka oy | Professional & scientific | 2017 |
| Muotoilutoimisto Helorinne & Kallio Oy | Professional & scientific | 1997 |
| Muotoilutoimisto Kairo Oy | Professional & scientific | 2004 |
| Muotoilutoimisto Tiistai Oy | Professional & scientific | 2001 |
| Muotoiluyhtiö Leeve Oy | Arts & recreation | 2018 |
| Muotolinja Oy | Real estate | 1976 |
| Muotomainos Oy | Professional & scientific | 1992 |
| Muotosuhde Oy | Professional & scientific | 2018 |
| Muototalo Bravoo Oy | Professional & scientific | 2007 |
| Muovikemia-Pkm Oy | Wholesale & retail | 1986 |
| Muovikilpi Oy | Manufacturing | 1975 |
| Muoviyhtymä Oy | Manufacturing | 1956 |
| Muppet Holding Oy | Financial services | 2017 |
| Muptax oy | Transport & logistics | 2020 |
| MurMurious Oy | Professional & scientific | 2019 |
| Muraba Oy | Construction | 2025 |
| Murak Oy | Construction | 2012 |
| Murasaki JEK Oy | Hospitality | 2023 |
| Murchello Oy | Wholesale & retail | 2021 |
| Murea Peura Oy | Financial services | 2022 |
| Murgitroyd & Company Limited, Filial i Finland | Professional & scientific | 2010 |
| Murina Oy | Arts & recreation | 2001 |
| Murmeli Finland Oy | Wholesale & retail | 1994 |
| Murmur Oy | Information & communication | 2002 |
| MuroLe CERAMICS Oy | Manufacturing | 2024 |
| MuroMed Oy | Health & social care | 2018 |
| Muromachi Suomi Oy | Hospitality | 2022 |
| Mursukasa Oy | Hospitality | 2005 |
| Murto & Kallio Oy | Construction | 2004 |
| Murtomaa Oy | Manufacturing | 2011 |
| Murtoniemen Merkki Oy | Financial services | 2004 |
| Murtotuulen TP Oy | Real estate | 2021 |
| Murtotuulen Tuulipuisto GP Oy | Financial services | 2019 |
| Murtotuulen Tuulipuisto Holding Ky | Financial services | 2021 |
| Murtotuulen Tuulipuisto Ky | Energy | 2019 |
| Murtovesi Oy | Professional & scientific | 2021 |
| Murtoviiva Oy | Construction | 2021 |
| Muru & Co. Oy | Hospitality | 2010 |
| Muru Agency Oy | Professional & scientific | 2023 |
| Muru Atelier Oy | Hospitality | 2012 |
| Muru Baby Food Oy | Wholesale & retail | 2017 |
| Muru Group Oy | Professional & scientific | 2026 |
| Muru Ravintolat Oy | Hospitality | 2021 |
| Muru Wines Oy | Wholesale & retail | 2018 |
| Muru-Dining Oy | Hospitality | 2008 |
| MuruPuru Oy | Wholesale & retail | 2016 |
| Muruseni Group Oy | Hospitality | 2025 |
| Muruseni Oy | Wholesale & retail | 2020 |
| Mus Oy | Hospitality | 2025 |
| Musa Ravintola Oy | Hospitality | 2025 |
| Musa-Joel Oy | Arts & recreation | 2025 |
| MusaEdu Avoin yhtiö | Arts & recreation | 2016 |
| Musab Oy | Transport & logistics | 2023 |
| Musafa Testing Oy | Transport & logistics | 2025 |
| Musafat Oy | Transport & logistics | 2026 |
| Musafir Oy | Administrative & support | 2022 |
| Musahotelli Oy | Real estate | 1991 |
| Musakka Adventures Oy | Professional & scientific | 2023 |
| Musakka Films Oy | Information & communication | 2022 |
| Musala Rakennus Oy | Construction | 2008 |
| Musamaailma Oy | Wholesale & retail | 1985 |
| Musan Aurinkovoima Oy | Energy | 2023 |
| Musatuotanto Helsinki Oy | Arts & recreation | 2017 |
| Musawi Capital Oy | Financial services | 2025 |
| Muscle Academy Oy | Education | 2019 |
| Muse Holding Oy | Financial services | 2021 |
| Musenn Technology Oy | Manufacturing | 2025 |
| Museokahvila Tove HAM Ab | Hospitality | 2026 |
| Museokuva Matti Huuhka & Co | Professional & scientific | 1981 |
| Muser Oy | Information & communication | 2024 |
| Mushap Oy | Hospitality | 2018 |
| Music Box Helsinki Oy | Information & communication | 2023 |
| Music Drive-In Oy | Education | 2014 |