| Arkkitehtitoimisto Seppo Markku Oy | Professional & scientific | 1991 |
| Arkkitehtitoimisto Sipponen, Teerenmaa Oy | Professional & scientific | 1974 |
| Arkkitehtitoimisto Tapani Vuorinen Oy | Professional & scientific | 1995 |
| Arkkitehtitoimisto Tupala Ky | Professional & scientific | 1977 |
| Arkkitehtitoimisto Vuopala Arkkitehdit Oy | Professional & scientific | 1996 |
| Arkkitehtuuritoimisto Seppo Peltomaa Oy | Professional & scientific | 2011 |
| Arktiira Oy | Professional & scientific | 1992 |
| Arkyhtymä Oy | Professional & scientific | 1994 |
| Arnis-Kirsty Oy | Hospitality | 2010 |
| Arofin Oy | Professional & scientific | 2023 |
| Aromitehdas Oy | Wholesale & retail | 2021 |
| Aron-Gent Palvelut Oy | Construction | 2019 |
| Arra Finland Oy | Information & communication | 2013 |
| Art Director Arkkitehdit Oy | Professional & scientific | 1995 |
| ArtMax Studio Oy | Other services | 2025 |
| ArtShop Finland Oy | Wholesale & retail | 2007 |
| Arte ja Orto Oy | Health & social care | 2001 |
| Artemore Oy | Professional & scientific | 2022 |
| Arthrone Oy | Wholesale & retail | 2008 |
| Artik-Rakenne avoin yhtiö | Construction | 1989 |
| Artik-Rakennuspalvelut avoin yhtiö | Construction | 2015 |
| Arto Jäppinen Ky | Information & communication | 1991 |
| Arvez Oy | Manufacturing | 2019 |
| Arviointitoimisto Oy Mikko Helenius & Co | Professional & scientific | 2011 |
| Arvokas Ihminen Oy | Education | 2021 |
| Asato Finland Oy | Professional & scientific | 1994 |
| Asemayhtiö Oy | Real estate | 2021 |
| Asennus Forum Oy | Construction | 1999 |
| Asennus Laurikainen Ky | Manufacturing | 1989 |
| Asennus-Kivelä Oy | Manufacturing | 1995 |
| Asennus-Saneeraus Sipox Oy Lahti | Construction | 1995 |
| Asennuspalvelu JyMe Oy | Construction | 2015 |
| Asennuspalvelu Martinmäki Oy | Construction | 2023 |
| Asfalttisalpa Oy | Construction | 2006 |
| Asianajotoimisto H. Puolakka Oy | Professional & scientific | 2011 |
| Asianajotoimisto Kurki-Suonio Oy | Professional & scientific | 1974 |
| Asianajotoimisto Lehti Oy | Professional & scientific | 2018 |
| Asianajotoimisto Lehtinen & Koponen Oy | Professional & scientific | 2007 |
| Asianajotoimisto Matti Kataja Ky | Professional & scientific | 1982 |
| Asianajotoimisto Minna Horelli Oy | Professional & scientific | 2009 |
| Asianajotoimisto Osmo Mäkinen Oy | Professional & scientific | 1977 |
| Asianajotoimisto Petteri Keinänen Oy | Professional & scientific | 2013 |
| Asianajotoimisto Päivi Kokko Oy | Professional & scientific | 2011 |
| Asianajotoimisto Saloranta Oy | Professional & scientific | 1990 |
| Asianajotoimisto Tiina Aalto Oy | Professional & scientific | 2018 |
| Asitracon Oy | Professional & scientific | 2018 |
| Asko Leppilampi Oy | Education | 1998 |
| Asko Virtanen Ky | Wholesale & retail | 1958 |
| Aspendos Oy | Hospitality | 1998 |
| Aspoint Oy | Manufacturing | 2018 |
| Assa Works Oy | Administrative & support | 2020 |
| Astax Oy Ab | Information & communication | 2026 |
| Asumisen Ilo Oy | Financial services | 2020 |
| Asumma Group Oy | Information & communication | 2021 |
| Ateljee Ompelimo Angelie Oy | Wholesale & retail | 2018 |
| Atepro Osaamispalvelut Oy | Education | 2017 |
| Ateriasisko Oy | Hospitality | 2021 |
| Athalay avoin yhtiö | Other services | 2013 |
| Atikka Oy | Professional & scientific | 2016 |
| Attendentes Uniq Oy | Health & social care | 2012 |
| Audeo Oy | Real estate | 1998 |
| Audiamond Osk | Information & communication | 2012 |
| Auditelle Oy | Professional & scientific | 2025 |
| Auditointi Laune Oy | Professional & scientific | 2021 |
| Auge Oy | Education | 2023 |
| Augustin Oy | Manufacturing | 1994 |
| Aukati Oy | Manufacturing | 1994 |
| Aulasmaa Invest Oy | Financial services | 2022 |
| Aumetek Oy | Manufacturing | 1988 |
| Aurelia Media Oy | Professional & scientific | 2021 |
| Aurevion Oy | Professional & scientific | 2026 |
| Aurinkotiimi Avoin yhtiö | Professional & scientific | 2004 |
| Aurivo Oy | Administrative & support | 2025 |
| Aurone Oy | Manufacturing | 2014 |
| Aurora Levels Oy | Professional & scientific | 2026 |
| Aurpro Ky | Professional & scientific | 1981 |
| Autiomaa Oy | Professional & scientific | 2010 |
| Auto Baja Oy | Other services | 1996 |
| Auto Her - Man Ky | Transport & logistics | 1978 |
| Auto performance oy | Wholesale & retail | 2022 |
| Auto-Alarm Finland Oy | Other services | 2021 |
| Auto-Lahti Ky Ari Kumpulainen | Wholesale & retail | 1999 |
| Auto-Sihlman Oy | Wholesale & retail | 2017 |
| Autohuolto Car-Pro Oy | Other services | 2008 |
| Autohuolto M Partanen Ky | Other services | 1994 |
| Autokorjaamo Matti Turtia Oy | Other services | 1994 |
| Autokorjaamo-Putkonen Ky | Other services | 1990 |
| Autokoulu Ajokortti Ky | Education | 1967 |
| Autokoulu Ohjaus Ky | Education | 1981 |
| Autoliike Fast Stock Oy | Wholesale & retail | 2020 |
| Automaalaamo Koskinen Oy | Other services | 1992 |
| Automaalaamo Rasi Oy | Other services | 2013 |
| Automaatio Rantanen Oy | Professional & scientific | 2014 |
| Autopesula Karlen Oy | Other services | 2016 |
| Autotalo J. Kolsi Oy | Wholesale & retail | 1995 |
| Autovinkkeli Ky | Wholesale & retail | 1988 |
| Avain- ja Lukkopalvelu Laune Oy | Wholesale & retail | 2013 |
| Avalus Oy | Information & communication | 2013 |
| Avan Oy | Wholesale & retail | 2013 |
| Avano Dreams Oy Ltd | Hospitality | 2019 |