| Arkkitehtitoimisto Marjut Lindqvist Ky | Professional & scientific | 1984 |
| Arkkitehtitoimisto Ulla Hovi Oy | Professional & scientific | 2003 |
| Arkkitehtuuri Jorma Mukala Ky | Professional & scientific | 1990 |
| Arktik Studio Oy | Professional & scientific | 1998 |
| Arrivac Oy | Professional & scientific | 2008 |
| Art Cubics avoin yhtiö | Real estate | 2026 |
| Arteliano Group Oy | Wholesale & retail | 2021 |
| Arvinsalmi Lautta Oy | Transport & logistics | 2017 |
| Asbesti- ja kiinteistösaneeraus Paldan Oy | Water & waste | 1995 |
| Asennus Ihatsu Oy | Manufacturing | 2003 |
| Asennuspojat LK Oy | Construction | 2015 |
| Asennuspojat Väntti Avoin yhtiö | Manufacturing | 2000 |
| Asianajotoimisto Advokatura Ky | Professional & scientific | 2021 |
| Asianajotoimisto Almgren & Sankamo Oy | Professional & scientific | 2020 |
| Asianajotoimisto Jari Tikka Ky | Professional & scientific | 1994 |
| Asianajotoimisto Timo Böhme Ky | Professional & scientific | 1998 |
| Askare Hallinto Oy | Administrative & support | 2013 |
| Askelen Group Oy | Information & communication | 2025 |
| Askeri Products Oy | Construction | 2002 |
| At Loei Thaifood Station Oy | Hospitality | 2022 |
| Ateriapalvelu Lounaspuisto Oy | Hospitality | 2022 |
| Atlantic Group Finland Ky | Construction | 2010 |
| Atsiam Consulting Oy | Professional & scientific | 2025 |
| Atte Yläsuutari OY | Construction | 2006 |
| Aubox Oy Kotka | Manufacturing | 1994 |
| Aucap Oy | Financial services | 1994 |
| Aumentas Oy | Information & communication | 2018 |
| Aurea Hoiva Oy | Health & social care | 2019 |
| Auris Bioenergia Holding Oy | Financial services | 2025 |
| Auris Bioenergia Oy | Energy | 2025 |
| Auris Energia Holding Oy | Financial services | 2015 |
| Auris Energia Oy | Financial services | 2015 |
| Auris Energiapalvelut Oy | Energy | 2017 |
| Auris Kaasuenergia Oy | Energy | 2017 |
| Auris Kaasunjakelu Oy | Energy | 2011 |
| Aurora Management Oy | Professional & scientific | 2020 |
| Auser Group Oy | Professional & scientific | 2025 |
| Auser Oy Kotka | Wholesale & retail | 2020 |
| Auto A-P Oy | Wholesale & retail | 2007 |
| Auto-Hipu, avoin yhtiö | Wholesale & retail | 1981 |
| Auto-Watti Ky | Other services | 1988 |
| AutoFin Oy | Wholesale & retail | 2021 |
| AutoTenttula Oy | Other services | 2020 |
| Autokoulu R. Snellman Ky | Education | 1981 |
| Automaalaamo Värikaara Oy | Other services | 2011 |
| Autotalon katsastus Oy | Transport & logistics | 2016 |
| Autovuokraamo Kunnas Ky | Administrative & support | 1986 |
| Avainvalmentajat Oy | Professional & scientific | 2025 |
| Avere Investment Oy Ltd. | Financial services | 2002 |
| Avinter Oy | Real estate | 2025 |
| Avireal Oy | Professional & scientific | 2003 |
| Avoin Yhtiö Kirsti ja Henrik Hänninen | Hospitality | 1989 |
| Avoin yhtiö Antti ja Kirsi Muuri | Manufacturing | 2000 |
| Avoin yhtiö Ekomin | Professional & scientific | 1991 |
| Avoin yhtiö KiuRT | Real estate | 2012 |
| Avoin yhtiö Kymen Hirsi- ja Kiinteistökeskus LKV | Wholesale & retail | 1999 |
| Avyv Oy | Wholesale & retail | 2021 |
| Azalea Maisemasuunnittelu Oy | Professional & scientific | 2005 |
| B K M-Loading Osakeyhtiö | Transport & logistics | 1998 |
| B. Skogberg Oy | Wholesale & retail | 2026 |
| BBQ Import Group Oy | Wholesale & retail | 2020 |
| BDB Finland Oy | Hospitality | 2024 |
| BGF Holding Oy | Information & communication | 2024 |
| Badger Works Oy | Information & communication | 2014 |
| Baja Oy | Health & social care | 2022 |
| BaltService Oy | Transport & logistics | 2013 |
| Bamse Kuljetus Oy | Transport & logistics | 2025 |
| Bardon Oy | Agriculture & fishing | 1989 |
| Battallion Logistics Oy | Transport & logistics | 2011 |
| BeamBrows Oy | Other services | 2019 |
| Begemc Ky | Construction | 2019 |
| Belafim Oy | Other services | 2008 |
| Belarna Oy | Hospitality | 2006 |
| Bemu huolto Kanerva avoin yhtiö | Other services | 2019 |
| Bergö Färja Oy | Transport & logistics | 2017 |
| Berloga Oy | Hospitality | 2022 |
| Best Alliance BA Oy | Transport & logistics | 2012 |
| Bestun Oy | Transport & logistics | 2023 |
| Betonijorma Oy | Professional & scientific | 2021 |
| Better Business Services Oy | Administrative & support | 1991 |
| Beuaty By Hertta Oy | Other services | 2024 |
| Big Foot Invest Oy | Real estate | 2018 |
| Bio Passage Ky | Professional & scientific | 1996 |
| Biomedical Finland Oy | Health & social care | 2011 |
| Bit Group Finland Oy | Information & communication | 2005 |
| Bittikarhu Oy | Information & communication | 2022 |
| Bittiäinen Oy | Information & communication | 1997 |
| Blue Cloud Consulting Oy | Professional & scientific | 2017 |
| Blue Fitness Hamina Oy | Arts & recreation | 2008 |
| Bluepeak Oy | Information & communication | 2019 |
| Boardstock Kommandiittiyhtiö | Wholesale & retail | 1992 |
| Bodwil Oy | Professional & scientific | 2013 |
| Bomba Oy | Manufacturing | 2014 |
| Bonusway Oy | Information & communication | 2011 |
| Bosset Oy | Construction | 2019 |
| Breath Oy | Information & communication | 2017 |
| Bridgemakers' Finnpeter Ltd Oy | Professional & scientific | 1995 |
| Brouskit Service OY | Construction | 2025 |
| Brunila Services Ky | Wholesale & retail | 2010 |
| Bulk Terminal Kotka Oy | Administrative & support | 2011 |