| Anni-Julia Oy | Professional & scientific | 2011 |
| Anterka Oy | Manufacturing | 1996 |
| Antkos Oy | Construction | 1988 |
| Anu Annikki Oy | Real estate | 2020 |
| Aploze Oy | Professional & scientific | 2015 |
| Apupal Oy | Construction | 2017 |
| ArVo Asuntohankinta Oy | Real estate | 2019 |
| Arctic Accounts Ky | Professional & scientific | 2000 |
| Arctic Breeze Oy | Professional & scientific | 2023 |
| Arctic Touch Finland Oy | Professional & scientific | 2018 |
| Ardano Oy | Financial services | 1991 |
| Argali Oy | Wholesale & retail | 2022 |
| Arimac Oy | Construction | 2008 |
| Arina & Yan Oy | Other services | 2019 |
| Aripa Kaiverrus Pykälä-aho Oy | Manufacturing | 1986 |
| Arjan Ruokaviestintä Oy | Arts & recreation | 2014 |
| Ark-Uur Tuotanto Oy | Manufacturing | 2009 |
| Arkkitehtitoimisto Arkas Oy | Professional & scientific | 2016 |
| Arkkitehtitoimisto Fogel-Michael Oy | Professional & scientific | 2007 |
| Arkkitehtitoimisto Jari Tamminen Oy | Professional & scientific | 1987 |
| Arkkitehtitoimisto Kekkonen & Vuorento Oy | Professional & scientific | 2006 |
| Arkkitehtitoimisto Vimma Oy | Professional & scientific | 2006 |
| Arman taito Oy | Other services | 2020 |
| Armian Oy | Real estate | 2011 |
| Arowa Oy | Professional & scientific | 1990 |
| Ars-Future Oy | Construction | 1989 |
| Arso Oy | Construction | 2024 |
| Art Amabile Oy | Information & communication | 1992 |
| Art Palis Oy | Administrative & support | 1991 |
| Asanad Oy | Information & communication | 2026 |
| Ascendum Oy | Real estate | 1987 |
| Asema X Oy | Hospitality | 2010 |
| Asennus Niinimaa Oy | Other services | 2005 |
| Asennus Rasimus Oy | Construction | 2022 |
| Asennus Toivonen Oy | Wholesale & retail | 1996 |
| Asennus-Santeri Oy | Construction | 2004 |
| Asianajotoimisto Kalle Ujainen Oy | Professional & scientific | 2019 |
| Asianajotoimisto Kinanen & Co Oy | Professional & scientific | 2021 |
| Asianajotoimisto Naturata Oy | Professional & scientific | 2016 |
| Asianajotoimisto Ulla-Riitta Kylli Oy | Professional & scientific | 2006 |
| Asianajotoimisto Wejberg & Wejberg | Professional & scientific | 1985 |
| Asiapromo Oy | Wholesale & retail | 2012 |
| Asiatieto T. Holopainen Oy | Arts & recreation | 1994 |
| Aslon Oy | Professional & scientific | 1979 |
| Astarena Oy | Wholesale & retail | 1997 |
| Asuste L & J Närhi, avoin yhtiö | Wholesale & retail | 1958 |
| Atacon Oy | Manufacturing | 2001 |
| Ataria Oy | Wholesale & retail | 2008 |
| Atlas Energia Oy | Professional & scientific | 2022 |
| Attaboy Workshop Oy | Wholesale & retail | 2016 |
| Audiovisual Systems of Finland Oy | Wholesale & retail | 1986 |
| Augnition Oy | Professional & scientific | 2019 |
| Auranta Oy | Professional & scientific | 2013 |
| Aurinko Energia Systems Oy | Construction | 2020 |
| Ausu-Osake Oy | Real estate | 1991 |
| Autiosalo Oy | Professional & scientific | 2019 |
| Auto Makkonen Oy | Wholesale & retail | 1986 |
| Auto Nordic Finland Oy | Wholesale & retail | 2025 |
| Auto-osake Oy | Professional & scientific | 2022 |
| Autohuolto Havukainen Oy | Other services | 2016 |
| Automaatio Curone Oy | Information & communication | 2026 |
| Automyynti Rantanen Oy | Wholesale & retail | 2022 |
| Autopaja Detroitista Itään Oy | Other services | 2018 |
| Autopeltikorjaamo Unto Mattila Ky | Other services | 1994 |
| Autosuojaamo Herranen Oy | Other services | 2014 |
| Autovarustelu Nice Car Ky | Other services | 1999 |
| Autoverkko.com Korjaamo Oy | Other services | 2017 |
| Autoverkko.com Oy | Wholesale & retail | 2018 |
| Avaimet Meidän Kotiin Oy | Real estate | 2026 |
| Aviator Media Oy | Professional & scientific | 2012 |
| Avoin yhtiö Kokkonen & Virkkunen | Wholesale & retail | 1997 |
| Axel-Engineering Oy | Real estate | 1990 |
| B & R Hunting Oy Ltd | Administrative & support | 2010 |
| B&R Holdings Oy | Administrative & support | 2021 |
| BC Capital Oy | Financial services | 2017 |
| Best-Caravan OY | Wholesale & retail | 2003 |
| BK-Napakka Kommandiittiyhtiö | Professional & scientific | 2000 |
| BL&A Kauneuskeskus Oy | Other services | 2016 |
| BRA Kiinteistöt Oy | Real estate | 2002 |
| BV Metalli Oy | Water & waste | 2002 |
| BX Erdoget Oy | Construction | 2022 |
| Baabeli Games Oy | Information & communication | 2026 |
| BaariBussi Oy | Arts & recreation | 2022 |
| BabyJo Oy | Financial services | 2025 |
| Baccola Oy | Financial services | 2000 |
| Bahiwera A Oy | Real estate | 2020 |
| BakAri Consulting Oy | Professional & scientific | 2016 |
| Baldrian Oy | Wholesale & retail | 1982 |
| Bar Pop In Oy | Hospitality | 2019 |
| Beauty & Wellness Sveitsi Oy | Other services | 2018 |
| Beauty Spa Sveitsi Oy | Other services | 2017 |
| Beckhoff Automation Oy | Wholesale & retail | 2000 |
| Beotek Oy | Construction | 1989 |
| Best-Set Oy | Other services | 1993 |
| Betoman Oy | Construction | 2025 |
| Betoni Virtanen Oy | Administrative & support | 1989 |
| Betonifabriikki Oy | Manufacturing | 2018 |
| Betonilattiatyöt M Pussinen Oy | Construction | 2005 |
| Binghatti Consulting Oy | Construction | 2026 |
| Binvestor Oy | Information & communication | 2018 |