| AnDeCon Oy | Professional & scientific | 2009 |
| AnJa Holding Oy | Real estate | 2023 |
| Anam Food Oy | Wholesale & retail | 2025 |
| Anemos Engineering Oy | Manufacturing | 2026 |
| Anorph Oy | Information & communication | 2026 |
| Ansion HR Oy | Administrative & support | 2025 |
| Ansocap Oy | Wholesale & retail | 2026 |
| Anssinkulma Imatra Avoin yhtiö | Real estate | 1994 |
| Antik & Design Gallery Tarvainen Oy | Wholesale & retail | 2025 |
| AnyCarCenter Oy | Other services | 1994 |
| ApeItTillYouMakeIt Oy | Financial services | 2024 |
| Apettas Oy | Information & communication | 2009 |
| Apritel Oy | Wholesale & retail | 2003 |
| Apugenius Oy | Manufacturing | 2020 |
| Aqua Vitae Oy | Water & waste | 1993 |
| Arctic Aesthetic Atelier Oy | Health & social care | 2026 |
| Arctic Cruises Oy | Transport & logistics | 2025 |
| Argo ATV Oy | Wholesale & retail | 2011 |
| Arhen Oy | Transport & logistics | 2002 |
| Arision Oy | Professional & scientific | 2023 |
| Arja Tolvanen Ky | Other services | 1985 |
| Arkkitehtistudio Sami Vuorinen Oy | Professional & scientific | 1992 |
| Arkkitehtisuunnittelu Petri Kemppinen Oy | Professional & scientific | 2001 |
| Arkkitehtitoimisto Klaus Pelkonen Oy | Professional & scientific | 1983 |
| Arkkitehtuuritoimisto Riitta ja Kari Ojala Oy | Professional & scientific | 1974 |
| Armpa Oy | Hospitality | 1997 |
| Arnora Oy | Professional & scientific | 2013 |
| Arrivio Oy | Professional & scientific | 2026 |
| Arvassalo Avoin yhtiö | Wholesale & retail | 2001 |
| Arvo Mustonen Oy | Agriculture & fishing | 1972 |
| Arvorakennus Oy | Construction | 2023 |
| As meza avoin yhtiö | Hospitality | 2020 |
| AsPal Oy T.Liimatta | Construction | 2025 |
| Asemaravintola Resiina Oy | Hospitality | 2013 |
| Asennuspaikka 28 Oy | Other services | 1992 |
| Asennuspalvelu Hellsten Oy | Manufacturing | 2017 |
| Asex Finland Oy | Administrative & support | 2019 |
| Asfur Ky | Manufacturing | 1987 |
| Asiamies J. Keinänen Oy | Transport & logistics | 2009 |
| Asianajotoimisto Heikki Oikkonen Oy | Professional & scientific | 2004 |
| Asianajotoimisto J Luukko Oy | Professional & scientific | 2023 |
| Asianajotoimisto Matti Hartikainen Ky | Professional & scientific | 1999 |
| Asianajotoimisto Saara Lukkarinen Oy | Professional & scientific | 2026 |
| Askele Oy | Professional & scientific | 2014 |
| Asset Vision Oy | Information & communication | 2006 |
| Assetti Oy | Information & communication | 2013 |
| Assi Group Oy | Real estate | 1968 |
| Astex Engineering Oy | Manufacturing | 1994 |
| Aston Kalmari Oy | Arts & recreation | 2021 |
| Asvi Oy | Other services | 1973 |
| Atsocon Oy | Professional & scientific | 2022 |
| AuCon Oy | Manufacturing | 2024 |
| Aurelia Turbines Oy | Manufacturing | 2013 |
| Auriferous Oy | Wholesale & retail | 2018 |
| Auringon Valo Ky Lappeenranta | Wholesale & retail | 2016 |
| Aurinkoauto Oy | Wholesale & retail | 2026 |
| Auto- ja Konehuolto Lappeenranta Oy | Other services | 2024 |
| Auto-Back Oy | Wholesale & retail | 1991 |
| Auto-Kilta Oy | Wholesale & retail | 2006 |
| Auto-Kilta Trucks Oy | Wholesale & retail | 2006 |
| Auto-Kilta Yhtiöt Oy | Wholesale & retail | 1987 |
| Auto-Matit avoin yhtiö | Other services | 1985 |
| Auto-Suni Oy | Wholesale & retail | 2000 |
| AutoExplore Oy | Information & communication | 2024 |
| AutoLap Oy | Other services | 2021 |
| AutoTrolling Oy | Information & communication | 2015 |
| Autokalustus Varho Ky | Wholesale & retail | 2005 |
| Autokorjaamo Life Oy | Other services | 2023 |
| Autokorjaamo Pamex Oy | Other services | 2016 |
| Autokoulu Drive Center Oy | Education | 1995 |
| Autokoulu Joensuu Ky | Education | 1968 |
| Automaalaamo Jukka & Hytti Oy | Other services | 1983 |
| Automeikkaus Litmanen Oy | Other services | 2007 |
| Autotalo Sollo Oy | Wholesale & retail | 2023 |
| Autovuokraamo P ja E Ojala Ky | Administrative & support | 1985 |
| Autovälitys Jantunen Ky | Wholesale & retail | 1984 |
| Avara Marketing Osuuskunta | Professional & scientific | 2023 |
| Avartas Oy | Health & social care | 2024 |
| Aveli Oy | Wholesale & retail | 2024 |
| Avernak Oy | Wholesale & retail | 2017 |
| Aviasport Areena Oy | Real estate | 2011 |
| Avoin Yhtiö Sarajärven Ura | Professional & scientific | 1994 |
| Avoin yhtiö Etelä-Karjalan Kehitystaito | Professional & scientific | 1992 |
| Avoin yhtiö Insinööritoimisto Georay | Professional & scientific | 1992 |
| Avoin yhtiö Koneurakointi Antti ja Matti Reijola | Construction | 1997 |
| Avoin yhtiö Pullin Leipomo | Manufacturing | 1989 |
| Avoin yhtiö Rauhansalo | Wholesale & retail | 2025 |
| Avoin yhtiö Veljekset Räihä | Agriculture & fishing | 1995 |
| Avustus ja Hoiva Tuija Oy | Health & social care | 2013 |
| Axelbond Oy | Professional & scientific | 1994 |
| B-Vision Oy | Wholesale & retail | 2012 |
| B2 Rent Oy | Real estate | 2024 |
| BC-Kauneus Oy | Real estate | 2020 |
| BCOL Oy | Wholesale & retail | 2001 |
| BH Development Oy | Financial services | 2021 |
| BK Bitumikermi-kattotyö Oy | Construction | 1991 |
| BKN Finland Oy | Real estate | 2025 |
| Boj Services OY | Transport & logistics | 2026 |
| BS-tukku Oy | Wholesale & retail | 2019 |
| Bualex OY | Construction | 2015 |