| Asianajotoimisto Castrén & Castrén Oy | Professional & scientific | 2023 |
| Asianajotoimisto Eeva-Leena Wendelin Oy | Professional & scientific | 2014 |
| Asianajotoimisto Eija Heikkinen Oy | Professional & scientific | 2014 |
| Asianajotoimisto Heikki Kukkonen sMBR Oy | Professional & scientific | 1992 |
| Asianajotoimisto Henna Honkakari Oy | Professional & scientific | 2018 |
| Asianajotoimisto Henri Lesonen Oy | Professional & scientific | 2023 |
| Asianajotoimisto Honkala Oy | Professional & scientific | 2025 |
| Asianajotoimisto Isoluoma Ky | Professional & scientific | 1993 |
| Asianajotoimisto Kalle Pyrhönen Oy | Professional & scientific | 2004 |
| Asianajotoimisto Kari Eriksson Oy | Professional & scientific | 1993 |
| Asianajotoimisto Katri Mäkinen Oy | Professional & scientific | 2013 |
| Asianajotoimisto Lapsiasiain Lakitalo Oy | Professional & scientific | 2011 |
| Asianajotoimisto Luolavirta Oy | Professional & scientific | 2011 |
| Asianajotoimisto Marja-Riitta Immonen Oy | Professional & scientific | 2012 |
| Asianajotoimisto Marjo Suoraniemi Ky | Professional & scientific | 1999 |
| Asianajotoimisto Marjut Hanhela Oy | Professional & scientific | 2020 |
| Asianajotoimisto Norra Oy | Professional & scientific | 1978 |
| Asianajotoimisto Ojala & Urpelainen Oy | Professional & scientific | 1991 |
| Asianajotoimisto Onnela-Kariniemi Oy | Professional & scientific | 2005 |
| Asianajotoimisto Pasi Hagman Oy | Professional & scientific | 2011 |
| Asianajotoimisto Pro Juridica Oy | Professional & scientific | 2009 |
| Asianajotoimisto Pöhö Oy | Professional & scientific | 1987 |
| Asianajotoimisto Regelin Oy | Professional & scientific | 2010 |
| Asianajotoimisto Sam Malinen Oy - Advokatbyrå Ab | Professional & scientific | 1985 |
| Asianajotoimisto Tolonen & Teittinen Oy | Professional & scientific | 1990 |
| Asianajotoimisto Verge Oy | Professional & scientific | 2023 |
| Asianajotoimisto Wallén-Leino Oy | Professional & scientific | 2010 |
| Asiantuntijakeskus GordionPro Oy | Professional & scientific | 2014 |
| Asire Oy | Financial services | 2009 |
| Askarctic Oy | Information & communication | 2019 |
| Askero Oy | Financial services | 2024 |
| Askutop Oy | Professional & scientific | 1998 |
| Asparon Oy | Real estate | 2017 |
| Aspen Laser Oy | Manufacturing | 2024 |
| Aspire Oy | Professional & scientific | 2008 |
| Assu Oy | Financial services | 2023 |
| Astan Oy | Other services | 2020 |
| Astanava Oy | Information & communication | 2011 |
| Astcon Oy | Real estate | 2020 |
| Astemet Oy | Real estate | 2014 |
| Asteroid Zone Software Oy | Information & communication | 2019 |
| Astrum International Oy Ltd | Construction | 1990 |
| Atelier Emilia K Oy | Professional & scientific | 2020 |
| Ateljee Haimila Oy | Professional & scientific | 1983 |
| Athlecon Oy | Education | 2026 |
| Atlafin Oy Ltd | Financial services | 2018 |
| Atlar Oy | Financial services | 2021 |
| Atnuus Health Oy | Information & communication | 2025 |
| Atomia OY | Professional & scientific | 2004 |
| Atomic Drop Games Oy | Manufacturing | 2017 |
| Attento Oy | Financial services | 2017 |
| Audiokauppa Oulu Oy | Wholesale & retail | 2013 |
| Audion Oy | Information & communication | 2025 |
| Auditkari Oy | Professional & scientific | 1995 |
| Augumenta Group Oy | Information & communication | 2024 |
| Augumin Oy | Health & social care | 2024 |
| Augustino Oy | Hospitality | 2024 |
| Auhai Oy | Hospitality | 2020 |
| Aukustin Oma Oy | Financial services | 2025 |
| Aumaint Oy | Construction | 2017 |
| Aunen Oy | Wholesale & retail | 2007 |
| AuraMed Oy | Health & social care | 2025 |
| Aurea Kodit Oy | Real estate | 2011 |
| Auringon Ajatus Oy | Wholesale & retail | 2018 |
| Auringonsade Oy | Health & social care | 2021 |
| Aurora Booleanis Oy | Information & communication | 2021 |
| Aurora DC Finland Oy | Information & communication | 2015 |
| Aurora DC Park Oy | Real estate | 2015 |
| Aurora Education Oy | Wholesale & retail | 2011 |
| Aurora Grand Oy | Administrative & support | 2026 |
| Aurora Marine Solutions Oy | Professional & scientific | 2022 |
| Aurora Pet Food Oy | Manufacturing | 2022 |
| Aurora Prospecting Oy | Mining & quarrying | 2026 |
| Aurora-Tuote Oy | Wholesale & retail | 2009 |
| AuroraTech Consultants Oy | Professional & scientific | 2024 |
| AutOulu Oy | Other services | 2020 |
| Autarkeia Investments oy | Real estate | 2019 |
| Autio Oy Infrapalvelut | Construction | 1975 |
| Autio Welding Oy | Professional & scientific | 2015 |
| Auto Jo-Ti Oy | Other services | 2009 |
| Auto ja Metallipojat Timo ja Raimo Takalahti | | 1982 |
| Auto- ja Maatalouskonekorjaamo Pussinen Ky | | 1985 |
| Auto-Profix Oy | Other services | 2003 |
| AutoJerry Partners Oy | Information & communication | 2015 |
| AutoLanginkoski Oy | Wholesale & retail | 2006 |
| AutoReklamaatio M. Ilola Oy | Professional & scientific | 2026 |
| Autofix1.com Oulu Oy | Other services | 2011 |
| Autohuolto Kurkela Oy | Other services | 2026 |
| Autohuolto Lohilahti Oy | Other services | 2014 |
| Autohuolto Äijä OY | Other services | 2022 |
| Autokorjaamo Mika Kaukko Oy | Other services | 2000 |
| Autokorjaamo Nikunen Oy | Other services | 1986 |
| Autokorjaamo UCCO Oy | Other services | 2016 |
| Autokoulu UCCO Oy | Education | 2015 |
| Autopaja Alppila Oy | Other services | 2022 |
| Autopalvelut CARANE Oy | Wholesale & retail | 2009 |
| Autopesu Juutinen Ky | Other services | 1993 |
| Autori Oy | Information & communication | 2010 |
| Autotallittajat Oy | Other services | 2026 |
| Autotalo Juntikka Vasaraperä Oy | Other services | 2026 |