| Arife Oy | Professional & scientific | 2010 |
| Arketon Oy | Construction | 2017 |
| Arki Oy | Real estate | 1987 |
| Arkiapu Olivia Oy | Health & social care | 2024 |
| Arkinen Oy | Administrative & support | 2025 |
| Arkistointipalvelu Signum Oy | Arts & recreation | 2023 |
| Arkkitehdit OK Oy | Professional & scientific | 1990 |
| Arkkitehtitoimisto Esa Piirainen Oy | Professional & scientific | 2014 |
| Arkkitehtitoimisto Lappalainen & Korjonen Oy | Professional & scientific | 1990 |
| Arkkitehtuuritoimisto A. Kärnä Oy | Construction | 1996 |
| Ars Laterna Oy | Wholesale & retail | 1997 |
| Artic Kiinteistöt Oy | Real estate | 2016 |
| Artic-Kaihdin Oy | Wholesale & retail | 2024 |
| Arto Järvinen Ky | Financial services | 2005 |
| Asennusliike J. Mononen Oy | Construction | 1985 |
| Asianajotoimisto Aki Pietarinen Oy | Professional & scientific | 1995 |
| Asianajotoimisto Ismo Nurmela Oy | Professional & scientific | 1995 |
| Asianajotoimisto Juka Oy | Professional & scientific | 2024 |
| Asianajotoimisto Jukka Ketonen Oy | Professional & scientific | 1987 |
| Asianajotoimisto Kai Laine Oy | Professional & scientific | 2008 |
| Asianajotoimisto Kontturi & Co Oy | Professional & scientific | 2004 |
| Asianajotoimisto LakiKarelia Oy | Professional & scientific | 2026 |
| Asianajotoimisto Lakipalvelu Petri Sallinen Oy | Professional & scientific | 1994 |
| Asianajotoimisto Martti Juvonen Oy | Professional & scientific | 1998 |
| Asianajotoimisto Nykänen & Vola Oy | Professional & scientific | 2025 |
| Asianajotoimisto Simonen & Savolainen Oy | Professional & scientific | 2025 |
| Asianajotoimisto Surakka Oy | Professional & scientific | 2019 |
| Asianajotoimisto Teräskulma Oy | Professional & scientific | 1994 |
| Asianajotoimisto Yrjö Kahelin Oy | Professional & scientific | 2008 |
| Asiantuntijapalvelut Heikki Päivinen Oy | Professional & scientific | 2019 |
| Assa Abloy Oy | Professional & scientific | 1997 |
| Atlas Bouncer Oy | Administrative & support | 2006 |
| Aurana Oy | Administrative & support | 2018 |
| Aurio Interiors Oy | Professional & scientific | 2024 |
| Auto Plauen Oy | Wholesale & retail | 1999 |
| Auto-Aatamila Oy | Wholesale & retail | 1990 |
| Auto-France Oy | Other services | 2022 |
| Auto-Hiisi Oy | Wholesale & retail | 2015 |
| Auto-Karjala Oy | Wholesale & retail | 2015 |
| Auto-Kuurna Oy | Real estate | 1977 |
| AutoFix Joensuu Oy | Other services | 2020 |
| AutoJaro Oy | Wholesale & retail | 2008 |
| AutoRitari Oy | Wholesale & retail | 2015 |
| AutoVisio Oy | Wholesale & retail | 2016 |
| Autoa Oy | Wholesale & retail | 2020 |
| Autoasennuspalvelu Immonen Ky | Other services | 1993 |
| Autoelektroniikka Könönen Ky | Other services | 1992 |
| Autohuolto Jukka Ryynänen Ky | Wholesale & retail | 2004 |
| Autohuolto Susiraja Oy | Other services | 2019 |
| Autojokeri Oy | Wholesale & retail | 2010 |
| Autokorjaamo Kari Turunen Ky | Other services | 1995 |
| Autokorjaamo Taskinen Oy | Other services | 2016 |
| Autokoulu AjoMesta Nuutinen Ky | Education | 1983 |
| Autokätevä Ky | Other services | 1981 |
| Autoliike Timo Lehikoinen Ky | Wholesale & retail | 1970 |
| Automaalaamo Kuormapojat Ky | Other services | 1986 |
| Automajuri Oy | Wholesale & retail | 2025 |
| Automyynti Veikko Laakkonen Oy | Wholesale & retail | 1995 |
| Autopalvelu JoeRent Oy | Administrative & support | 2017 |
| Autopalvelu Koponen Oy | Transport & logistics | 2000 |
| Autopalvelut Keronen Oy | Other services | 2015 |
| Autopurkaamo Karjalan Purku-Pojat Oy | Wholesale & retail | 1981 |
| Autovaltonen Ky | Wholesale & retail | 2010 |
| Avain Invest Oy | Real estate | 2016 |
| AvainKeittiöt Oy | Wholesale & retail | 2019 |
| Avanto Assets Oy | Administrative & support | 2026 |
| Avanto Club Oy | Financial services | 2025 |
| Avantosauna Kuura Oy | Arts & recreation | 2022 |
| Avaruusasema Oy | Professional & scientific | 2026 |
| Avoin yhtiö Al-Amin | Hospitality | 2003 |
| Avoin yhtiö Kinnunen & Sorsa | Wholesale & retail | 1995 |
| Avoin yhtiö pienryhmäpäiväkoti Väkkärä | Health & social care | 1995 |
| Azets Document Solutions Oy | Information & communication | 2014 |
| B-Art Oy | Health & social care | 2012 |
| Bag Chasers OY | Financial services | 2024 |
| BAMBOO Oy | Arts & recreation | 2020 |
| BI-Group Oy | Professional & scientific | 2025 |
| BKB Consulting & Accounting Oy | Professional & scientific | 2025 |
| BLC Turva Oy | Wholesale & retail | 1999 |
| BNagomi Group Oy | Financial services | 2026 |
| BNagomi Oy | Education | 2026 |
| Bad Bee Fix Oy | Other services | 2021 |
| Baranda Oy | Hospitality | 2025 |
| Barsanen Oy | Professional & scientific | 2015 |
| Bayes Helsinki Oy | Professional & scientific | 2020 |
| Be5 Oy | Wholesale & retail | 2025 |
| Bearfell Oy | Wholesale & retail | 2021 |
| Beauty Minds - Beati Mites Oy | Other services | 2023 |
| Beauty Services Minna Oy | Other services | 2024 |
| Benefactor Partners Oy | Administrative & support | 2021 |
| Beneseer Oy | Information & communication | 2021 |
| BetoFin Rakennus Oy | Construction | 2016 |
| Betoni timpurit oy | Construction | 2024 |
| BiiMer Oy | Other services | 2024 |
| Biker School Joensuu Oy | Education | 2017 |
| Bikeri Oy | Administrative & support | 2021 |
| Bilberry Ky | Education | 2005 |
| Binderholz Nordic Oy | Manufacturing | 2014 |
| Binomi Oy | Manufacturing | 2011 |
| Biodo Oy | Professional & scientific | 2014 |