| Asag rakennus Oy | Construction | 2024 |
| Asappi Oy | Transport & logistics | 2002 |
| Asbestidiili Oy | Construction | 2019 |
| Ascensia Diabetes Care Finland Oy | Wholesale & retail | 2015 |
| Aseliike Kärki OY | Wholesale & retail | 2024 |
| Asemamiehenkadun Pysäköinti Oy | Transport & logistics | 2019 |
| Asennus Randelin Oy | Construction | 1999 |
| Asennus Taalas Oy | Construction | 2021 |
| Asennus Tikkanen Ky | Administrative & support | 2007 |
| Asennus-Mati Oy | Construction | 2007 |
| AsennusKauppinen Oy | Construction | 2023 |
| Asennusnikkari Oy | Construction | 1995 |
| Asennustekniikka Malmberg & Räikkönen Oy | Construction | 2011 |
| Asennustoimitus Pro Oy | Manufacturing | 2022 |
| Asennustrio Oy | Construction | 2024 |
| Asenso Oy | Information & communication | 2023 |
| Asepi Oy | Other services | 2025 |
| Aseta Oy | Wholesale & retail | 1993 |
| Asfaltti Sivén Häme Oy | Construction | 2023 |
| Asfaltti Sivén Oy | Construction | 2014 |
| Asfalttikallio Oy | Construction | 2012 |
| Asfalttilinja Oy | Construction | 2016 |
| Asfalttitaipale Oy | Construction | 1973 |
| Asiakasankkuri Oy | Professional & scientific | 2025 |
| Asiakasmedia Jaatinen Oy | Professional & scientific | 2022 |
| Asian Ocean Oy | Hospitality | 2015 |
| Asianajotoimisto Aaro Loikkanen Ky | Professional & scientific | 1992 |
| Asianajotoimisto Alex Oy | Professional & scientific | 1990 |
| Asianajotoimisto Andström Oy | Professional & scientific | 1989 |
| Asianajotoimisto Defenda Oy | Professional & scientific | 2025 |
| Asianajotoimisto Elo & Meriläinen Oy | Professional & scientific | 2015 |
| Asianajotoimisto Haanpää Oy | Professional & scientific | 2018 |
| Asianajotoimisto Honkanen & Piispanen Oy | Professional & scientific | 2018 |
| Asianajotoimisto J. Rajamäki Oy | Professional & scientific | 2008 |
| Asianajotoimisto Jurentia Oy | Professional & scientific | 2006 |
| Asianajotoimisto Kokko & Tiainen Oy | Professional & scientific | 1991 |
| Asianajotoimisto Kouhia Oy | Professional & scientific | 2023 |
| Asianajotoimisto LakimiesCom Oy | Professional & scientific | 2002 |
| Asianajotoimisto Lavonen Oy | Professional & scientific | 2015 |
| Asianajotoimisto Leena Partanen Oy | Professional & scientific | 1997 |
| Asianajotoimisto Lex Moor Oy | Professional & scientific | 2013 |
| Asianajotoimisto Linninen Oy | Professional & scientific | 2000 |
| Asianajotoimisto Markku Jakobsson Oy | Professional & scientific | 1996 |
| Asianajotoimisto Niemi & Puhakka Oy | Professional & scientific | 2023 |
| Asianajotoimisto Olli Piipponen Oy | Professional & scientific | 1996 |
| Asianajotoimisto Sirpa Lumme Oy | Professional & scientific | 1993 |
| Asiantuntijakeskus Lehtisalo Oy | Professional & scientific | 2005 |
| Asiantuntijapalvelut J-P Launne Oy | Professional & scientific | 1996 |
| Asiantuntijapankki Oy | Professional & scientific | 2025 |
| Asidom Equipment Oy Ab | Wholesale & retail | 2021 |
| Asikaisen Puoti Oy | Wholesale & retail | 2021 |
| Askal Technology Oy | Manufacturing | 2025 |
| Askel kehittämiseen Oy | Education | 2017 |
| Askiston autokorjaamo Oy | Other services | 2026 |
| Askolan Kotolämpö Oy | Real estate | 1976 |
| Aslakin Kauppa Oy | Financial services | 1976 |
| Aslan Pizzeria avoin yhtiö | Hospitality | 2025 |
| Aspa Marketing Solutions Oy | Professional & scientific | 2024 |
| Aspen Capital Oy | Financial services | 2017 |
| Aspen Systems Oy | Information & communication | 2024 |
| Assa Abloy Entrance Systems Finland Oy | Wholesale & retail | 1963 |
| Assemblin Oy | Construction | 2006 |
| Assistor Oy Ab | Other services | 2019 |
| Astedrone Oy | Information & communication | 2016 |
| Astiavuokraus Mattimauste Oy | Administrative & support | 2018 |
| Astor Oy Matkapalvelu Travelservice | Administrative & support | 1997 |
| Astoros Oy | Wholesale & retail | 2002 |
| Astrac Oy | Construction | 2024 |
| Asuma Palvelut Oy | Administrative & support | 1970 |
| Asunnot Kuronen Oy | Real estate | 2021 |
| Asunnot ja Kiinteistöt Uusimaa Oy | Real estate | 2016 |
| At Projektinhallinta Oy | Professional & scientific | 2021 |
| Atak Group Oy | Wholesale & retail | 2025 |
| Atao Oy | Information & communication | 2009 |
| Atap-Huolto Oy | Wholesale & retail | 2015 |
| Atavaranet Oy | Transport & logistics | 2024 |
| Atea Finance Oy | Financial services | 2007 |
| Atea Finland Holding Oy | Wholesale & retail | 2007 |
| Atea Finland Oy | Wholesale & retail | 1993 |
| Atelpuu Oy | Construction | 2026 |
| Aterto Oy | Construction | 2017 |
| Athletiq Oy | Wholesale & retail | 2026 |
| Atik Oy | Other services | 2019 |
| Atithi Oy | Hospitality | 2017 |
| AtlantisFX Oy | Wholesale & retail | 2021 |
| Atlas Dominus Oy | Financial services | 2026 |
| Atlas One Oy | Professional & scientific | 2016 |
| Atlas agency Oy | Professional & scientific | 2025 |
| Atnarolas Oy | Real estate | 2000 |
| Atolli Oy | Wholesale & retail | 1989 |
| Atonal Designs Oy | Professional & scientific | 2015 |
| Atop-Tieto Oy | Information & communication | 1987 |
| Attilan Enterprises Oy | Information & communication | 2023 |
| Atusa Cash & Curry Oy | Wholesale & retail | 2023 |
| Atzait Oy | Information & communication | 2022 |
| Aubas Oy | Education | 2022 |
| Audit Raittinen Oy | Professional & scientific | 2025 |
| Auditive Edu Oy | Arts & recreation | 2013 |
| Aufwin Capital Oy | Financial services | 2025 |
| Aufwin Defence Systems Oy | Manufacturing | 2020 |