| AuroraLine Oy | Transport & logistics | 2026 |
| AuroraMove Oy | Transport & logistics | 2024 |
| AuroraSky Oy | Professional & scientific | 2023 |
| Auroral Oy | Health & social care | 2015 |
| Auroran Komiikka Oy | Arts & recreation | 2024 |
| Auroratalo Oy | Real estate | 2009 |
| AuruAudio Oy | Information & communication | 2012 |
| Aurum Medicine Oy | Health & social care | 2025 |
| Aurun Oy | Professional & scientific | 2013 |
| Ausade Holding Oy | Real estate | 2006 |
| Ausel Oy | Real estate | 1993 |
| Ausmet Oy | Manufacturing | 2020 |
| Auspex Oy | Information & communication | 1984 |
| Auteknik Oy | Wholesale & retail | 2018 |
| Autere Films Oy | Information & communication | 2021 |
| Authalla Oy | Information & communication | 2026 |
| Authentic Leadership Consulting ALC Oy | Education | 2017 |
| Authentic Pilates Center Ky | Education | 2015 |
| Authentic Sounds Oy | Information & communication | 2013 |
| Authentic Wines Finland Oy | Wholesale & retail | 2024 |
| Authman Invest Oy | Financial services | 2019 |
| Auticon Oy | Information & communication | 2019 |
| Autio Associates Ltd Oy | Professional & scientific | 1996 |
| Autio Legal Oy | Professional & scientific | 2006 |
| Autio Partners Ltd Oy | Professional & scientific | 2010 |
| Autiosaari Oy | Professional & scientific | 2020 |
| Autismisäätiön kiinteistöt oy | Real estate | 2002 |
| Auto - Muovi Oy KEM | Wholesale & retail | 1989 |
| Auto - Poutiainen Oy | Other services | 1997 |
| Auto Apu AM OY | Manufacturing | 2025 |
| Auto Areco Oy | Transport & logistics | 1995 |
| Auto Arikko Oy | Other services | 2001 |
| Auto Capital Oy | Wholesale & retail | 2006 |
| Auto Garden Oy | Other services | 1993 |
| Auto Karvisa Oy | Other services | 2025 |
| Auto MHR Oy | Wholesale & retail | 2013 |
| Auto Sky Oy | Other services | 2021 |
| Auto Trade Finland Oy | Wholesale & retail | 2011 |
| Auto Virtuaali Oy | Wholesale & retail | 2009 |
| Auto-Arena Oy | Financial services | 1973 |
| Auto-Ekroos Oy | Wholesale & retail | 1965 |
| Auto-Harraste Oy | Other services | 1981 |
| Auto-Help Oy Helsinki | Other services | 1997 |
| Auto-Jagge Helsinki Oy | Wholesale & retail | 2026 |
| Auto-Pika Oy | Other services | 1982 |
| Auto-Uuttera Oy | Other services | 2001 |
| Auto-Wihuri Oy | Manufacturing | 1969 |
| Auto-spa valimotie oy | Other services | 2023 |
| Auto28 Oy | Wholesale & retail | 2019 |
| AutoBil Espoo avoin yhtiö | Wholesale & retail | 2009 |
| AutoCenter Finland Oy | Other services | 2023 |
| AutoCherry Oy | Manufacturing | 2024 |
| AutoConcept Insurance AB - Filial Finland | Financial services | 2012 |
| AutoDent Oy | Other services | 2005 |
| AutoDent PDR Oy | Other services | 2016 |
| AutoDent Raisio Oy | Other services | 2021 |
| AutoFuse Oy | Wholesale & retail | 2025 |
| AutoHaus Boost Oy | Other services | 2016 |
| AutoLoop Oy | Information & communication | 2025 |
| AutoMaster Car Service Oy | Other services | 2024 |
| AutoMinttiin Oy | Other services | 2023 |
| AutoPlaza Oy | Wholesale & retail | 1998 |
| AutoSawit Technology Oy | Manufacturing | 2021 |
| AutoStudio Oy | Wholesale & retail | 1986 |
| Autocar Alu Ky | Manufacturing | 2012 |
| Autocurrus Oy | Transport & logistics | 1962 |
| Autodemy Oy | Other services | 2015 |
| Autodesk Finland Oy | Information & communication | 2020 |
| Autoenergy Oy | Other services | 2013 |
| Autoexpo Oy | Wholesale & retail | 2003 |
| Autoextra Helsinki Oy | Other services | 2023 |
| Autofix Center Oy | Other services | 2026 |
| Autohamsteri Oy | Administrative & support | 1997 |
| Autohaus Helsinki Oy | Wholesale & retail | 2020 |
| Autohuolto 247 Oy | Other services | 2020 |
| Autohuolto Aritin Oy | Other services | 2019 |
| Autohuolto Arvi Hämäläinen Oy | Wholesale & retail | 1978 |
| Autohuolto Canoma Oy | Other services | 2010 |
| Autohuolto Kari Backman Ky | Wholesale & retail | 1981 |
| Autohuolto Rex Oy | Other services | 2024 |
| Autohuolto T Selviranta Ky | Wholesale & retail | 1980 |
| Autohuolto TamCar Oy | Other services | 2015 |
| Autohuolto VolFix Oy | Other services | 2020 |
| Autokalustehuolto Oy | Real estate | 1972 |
| Autokeskus Oy | Wholesale & retail | 1997 |
| Autokorjaamo Alex Oy | Other services | 2010 |
| Autokorjaamo Ant-Auto Ky | Other services | 2003 |
| Autokorjaamo Jarrupoljin Oy | Other services | 1993 |
| Autokorjaamo K. Rytinki Oy | Other services | 1979 |
| Autokorjaamo Kaari Oy | Other services | 2024 |
| Autokorjaamo Kari Järvinen Oy | Other services | 2011 |
| Autokorjaamo Koskela Oy | Other services | 2003 |
| Autokorjaamo Merihaka Oy | Other services | 2025 |
| Autokorjaamo Metsälä Oy | Other services | 2021 |
| Autokorjaamo P.Rouhimo Oy | Other services | 2001 |
| Autokorjaamo Volkan Oy | Other services | 2024 |
| Autokorjaamo Ysom Oy | Other services | 2021 |
| Autokoulu Akseli Oy | Education | 2015 |
| Autokoulu Aulis Oy | Education | 1978 |
| Autokoulu E Nygård Oy | Education | 1962 |