| Oy MTG-Consulting Ltd | Helsinki | 2020 |
| Oy MVM-Projects Ltd | Lusi | 1996 |
| Oy Mageia Ab | Espoo | 2002 |
| Oy Magic Moment Technology Ltd | Vöyri | 1989 |
| Oy Magna Carta Ab | Helsinki | 1991 |
| Oy Magnificus Ab | Helsinki | 1991 |
| Oy Magnum Finland Ltd. | Tampere | 1990 |
| Oy Magnus Svennblad Ab | Karjaa | 1997 |
| Oy Magnussen Ab | Helsinki | 2008 |
| Oy Maher Ltd | Helsinki | 2016 |
| Oy Mahlberg & Mahlberg Ab | Espoo | 2013 |
| Oy Mainos UP | Helsinki | 1966 |
| Oy Mainos-Reklam Peter Lundström Ab | Vaasa | 1981 |
| Oy Mainoskonttori Helmi Ab | Helsinki | 1981 |
| Oy Mainostoimisto Bock's Office Ab | Vaasa | 1989 |
| Oy Mammut Ab mainosateljee | Helsinki | 1960 |
| Oy Man & Horsepower Services Ltd | Pietarsaari | 2004 |
| Oy Management Services Scandinavia Ab | Luoma | 1987 |
| Oy Manarola Ab | Helsinki | 2009 |
| Oy Manial Finans Ab | Helsinki | 1990 |
| Oy Mar AN Dragsfjärd Ab | Dragsfjärd | 1990 |
| Oy Marbeck Productions Ltd | Helsinki | 1995 |
| Oy Marea Ltd | Hanko Pohjoinen | 2012 |
| Oy Mariners' Assistance Ltd., Ab | Koskenpää | 1990 |
| Oy Marinex Ab | Hirvlax | 1989 |
| Oy Maritop Ab | Porvoo | 2002 |
| Oy Market Touch Ltd | Tampere | 1995 |
| Oy Market-Trading House Helsinki Ltd. | Espoo | 1989 |
| Oy Marks & Marks Consulting | Espoo | 1994 |
| Oy Masaki-Consulting Ab | Turku | 1988 |
| Oy Mastemas Ltd | Vihti | 1996 |
| Oy Master Mariner Ltd. | Turku | 1998 |
| Oy Matikainen Consulting Ltd | Helsinki | 2004 |
| Oy Matti Kojo Ab | Degerby | 2013 |
| Oy Mawiro Ab | Jorvas | 1990 |
| Oy Max Lindfors Ab | Osoite Tuntematon | 2012 |
| Oy Mazzonas Ab | Evitskog | 1988 |
| Oy Meaning Processing Ltd | Helsinki | 2005 |
| Oy Medfiles Ltd | Vantaa | 1995 |
| Oy Mediafocus Ab | Helsinki | 1995 |
| Oy Medical Advisory Services Medaser Ltd | Helsinki | 1987 |
| Oy Meelitus Ab | Turku | 1998 |
| Oy Mega Alfa Ab | Helsinki | 1989 |
| Oy Mega Delta Ab | Helsinki | 1989 |
| Oy Mega Gamma Ab | Helsinki | 1989 |
| Oy Megawell Ab | Helsinki | 1989 |
| Oy Melior Pharma Ab | Vaasa | 2019 |
| Oy Mellifera Ab | Liljendal | 1986 |
| Oy Meninx Ltd | Kuopio | 1995 |
| Oy Mente Marine Ab | Vaasa | 1993 |
| Oy Mercato Esperto FI Ltd | Siltakylä | 1993 |
| Oy Merenge Ab | Siuntio | 1991 |
| Oy Merinova Ab | Vaasa | 1989 |
| Oy Mermaid Ab | Helsinki | 1989 |
| Oy Micoltech Ab | Raisio | 2006 |
| Oy Microalfa Ab | Helsinki | 1989 |
| Oy Microdelta Ab | Helsinki | 1989 |
| Oy Microgamma Ab | Helsinki | 1989 |
| Oy Mind Art & Design Ltd | Tuusula | 1994 |
| Oy Mirotec Ltd | Riihimäki | 1987 |
| Oy Mittkontakt ab | Närpiö As | 1987 |
| Oy Mobicraft Ab | Turku | 1993 |
| Oy Mobilium Ltd | Helsinki | 2006 |
| Oy Modilis Labs | Helsinki | 2010 |
| Oy Mondo-Export Ltd | Merikaarto | 1997 |
| Oy MoneyRiff Corp. | Lapua | 2024 |
| Oy Moneylab Ltd | Osoite Tuntematon | 1992 |
| Oy Monkisland Ab | Helsinki | 2012 |
| Oy Montall Ab | Helsinki | 1990 |
| Oy Moontainer Ab | Turku | 1998 |
| Oy Morgan Consulting Ab | Espoo | 2005 |
| Oy Mortti & Valtanen | Helsinki | 2026 |
| Oy Musta Granit | Helsinki | 1915 |
| Oy NAREMA Ab | Närpiö | 2019 |
| Oy NW Holding Ab | Helsinki | 2007 |
| Oy Nalle Grönberg Ab | Inkoo | 2019 |
| Oy Namento Ab | Vaasa | 1996 |
| Oy Nancotex Ab | Isojoki | 1990 |
| Oy Narda International Ltd | Helsinki | 1989 |
| Oy Naturnus Ltd | Helsinki | 2008 |
| Oy Naumecon Ltd | Espoo | 1990 |
| Oy Neema Ab | Helsinki | 2022 |
| Oy Neptunusweld Ltd | Nuutajärvi | 1997 |
| Oy Nerual Ab | Helsinki | 2000 |
| Oy Netpac Ab | Hanko | 2020 |
| Oy Network Team Finland ARS Ab | Espoo | 1993 |
| Oy Neuromed Ab | Helsinki | 1994 |
| Oy New Bike Ltd | Helsinki | 2018 |
| Oy Nicall Ab | Inkoo | 2019 |
| Oy NiceThings Ab | Vaasa | 2009 |
| Oy Nintec Ab | Poikko | 1990 |
| Oy Nivilu Ab | Espoo | 2005 |
| Oy Noble Group Ltd | Helsinki | 1991 |
| Oy Noble Information Ltd | Helsinki | 1988 |
| Oy Noble Services Ltd | Helsinki | 1988 |
| Oy Noice Light Ltd | Helsinki | 1996 |
| Oy Nominee Ab | Helsinki | 1990 |
| Oy Nord Hyforce Systems Ltd | Kotka | 2001 |
| Oy Nordic Advisory Services Ab | Helsinki | 2020 |
| Oy Nordic BIM IPR Holding Ab | Helsinki | 2025 |