| Oy K Nyberg Ab | Construction | 2000 |
| Oy KB Corporation Ab | Professional & scientific | 2010 |
| Oy KB Transport Ab | Real estate | 1990 |
| Oy KFM Accounting Ltd | Professional & scientific | 1992 |
| Oy KH-Karixmatic Ltd | Wholesale & retail | 1990 |
| Oy Kaj Hellman Ltd. | Wholesale & retail | 1977 |
| Oy Kannonkari | Wholesale & retail | 1986 |
| Oy Kansio-Aitta Ab | Manufacturing | 1991 |
| Oy Kara-Steel Ltd | Wholesale & retail | 2000 |
| Oy Kari Lampén & Co Ab | Transport & logistics | 2001 |
| Oy Kataprik Ab | Financial services | 1977 |
| Oy Kauklahden Hammaslääkärit-Köklax Tandläkare Ab | Health & social care | 2012 |
| Oy Kehä Nortek Ab | Administrative & support | 1997 |
| Oy Kesef Ab | Wholesale & retail | 1991 |
| Oy Kilon talli - Kilo stall Ab | Education | 1980 |
| Oy Kimifinn Ltd | Administrative & support | 2005 |
| Oy Kiva-Rakenne Ab | Professional & scientific | 1994 |
| Oy Kivipylvään Puisto - Märkesstens Parken Ab | Real estate | 1998 |
| Oy Koivumankkaan Sähkö Ab | Construction | 2004 |
| Oy Kontutek Ab | Wholesale & retail | 1987 |
| Oy Korpilampi Ab | Hospitality | 1998 |
| Oy Koskenkylän Sähkökuja 3 | Real estate | 2018 |
| Oy Kotitoimi Ab | Wholesale & retail | 2014 |
| Oy Kovanen Group Worldwide Ltd. | Wholesale & retail | 1946 |
| Oy Krax-invest Ab | Financial services | 2021 |
| Oy Kvalitetbil FIN Ab | Wholesale & retail | 2021 |
| Oy Köppinen Ab | Wholesale & retail | 1984 |
| Oy LIVIO JOY Ltd | Education | 2021 |
| Oy Landox Ab | Wholesale & retail | 1989 |
| Oy Lantinki Ab | Real estate | 1976 |
| Oy Laudo Ab | Construction | 1979 |
| Oy Lehtimainos - Pressreklam Ab LP | Professional & scientific | 1982 |
| Oy Lemon Company Ltd | Professional & scientific | 2008 |
| Oy Leonis Ab | Information & communication | 1969 |
| Oy Libart Ab | Professional & scientific | 1990 |
| Oy Lifvet Ab | Professional & scientific | 2022 |
| Oy Liikunta- ja Vapaa-ajankeskus Nuuksio-Noux Ab | Professional & scientific | 1989 |
| Oy Lindab Ab | Wholesale & retail | 1993 |
| Oy Linde Gas Ab | Manufacturing | 1917 |
| Oy Lindholm Lines Ab | Transport & logistics | 1987 |
| Oy Linna TC Ltd | Wholesale & retail | 1994 |
| Oy Lipastor Ab | Real estate | 1990 |
| Oy Lonepinehill Ltd | Professional & scientific | 2022 |
| Oy Lumocon Ab | Professional & scientific | 2025 |
| Oy Lux Ab | Wholesale & retail | 2025 |
| Oy Lux Mineral Services Ab | Wholesale & retail | 2020 |
| Oy Lännen Tutkimus - Western Research Inc | Professional & scientific | 1994 |
| Oy M. Nokio Ltd | Wholesale & retail | 1987 |
| Oy MAS-Produktion Ltd | Real estate | 1989 |
| Oy MAX Kaupantekijät | Wholesale & retail | 1995 |
| Oy MG-Trading Ab | Wholesale & retail | 1985 |
| Oy MK-Nordtech Ltd | Other services | 1994 |
| Oy MMM Solutions Ltd | Arts & recreation | 2023 |
| Oy MP-Group Ltd | Manufacturing | 1985 |
| Oy MWH Management Ltd | Financial services | 1987 |
| Oy Mageia Ab | Professional & scientific | 2002 |
| Oy Mahlberg & Mahlberg Ab | Professional & scientific | 2013 |
| Oy Makrill Suomi | Manufacturing | 1996 |
| Oy Malmcon Ab | Information & communication | 2014 |
| Oy Mariar Consultants Ltd | Wholesale & retail | 1991 |
| Oy Market-Trading House Helsinki Ltd. | Professional & scientific | 1989 |
| Oy Marks & Marks Consulting | Professional & scientific | 1994 |
| Oy Maxrona Control Ab | Financial services | 1994 |
| Oy Mec-Port Ab | Wholesale & retail | 1974 |
| Oy Med Diagnosis Ltd | Wholesale & retail | 2024 |
| Oy Medifon Ab | Wholesale & retail | 1981 |
| Oy Meditellus Ab | Health & social care | 1996 |
| Oy Medix Biochemica Ab | Manufacturing | 1998 |
| Oy Medosec Ab | Health & social care | 2025 |
| Oy Meikka Invest Ab | Financial services | 1989 |
| Oy Menita Ab | Wholesale & retail | 1960 |
| Oy Mercurius Capital Ab | Financial services | 2023 |
| Oy Metalli R. Rautanen | Wholesale & retail | 1979 |
| Oy Metsäuuttu Ab | Construction | 2025 |
| Oy Mi-Card Ab | Information & communication | 1988 |
| Oy Moccamaster Nordic Ab | Wholesale & retail | 2011 |
| Oy Modaki Ab | Transport & logistics | 1990 |
| Oy Mogador Ab | Real estate | 1990 |
| Oy Monero Servo Finland Ltd | Wholesale & retail | 2017 |
| Oy Morgan Consulting Ab | Professional & scientific | 2005 |
| Oy Muovituote Ab | Manufacturing | 1950 |
| Oy Murator Ab | Construction | 2002 |
| Oy My Happy Days Ltd | Information & communication | 2017 |
| Oy Mäntytonttu | Real estate | 1974 |
| Oy NC Bothnia Management Ab | Transport & logistics | 1990 |
| Oy NH Creations Ab | Other services | 2013 |
| Oy Nappe Ab | Health & social care | 2004 |
| Oy Natura-Vitamins Ltd Ab | Wholesale & retail | 1990 |
| Oy Naumecon Ltd | Professional & scientific | 1990 |
| Oy Navarco Nord Ltd | Construction | 1990 |
| Oy Nefab Ab | Manufacturing | 1987 |
| Oy Nelikuukkeli | Real estate | 1983 |
| Oy Nerival Group Ab | Wholesale & retail | 2000 |
| Oy Network Team Finland ARS Ab | Professional & scientific | 1993 |
| Oy Niklashipping Ltd | Transport & logistics | 1989 |
| Oy Nissflower Ab | Wholesale & retail | 2018 |
| Oy Nivilu Ab | Professional & scientific | 2005 |
| Oy Nordinfo Ab | Professional & scientific | 1988 |
| Oy Noux Consulting Ab | Professional & scientific | 1998 |
| Oy O & E Tallberg Ab | Construction | 1997 |