| AtoMil Oy | Financial services | 2015 |
| Aturnus Oy | Administrative & support | 2026 |
| Audit & Invest Kouvola Oy | Financial services | 1984 |
| Auriel Oy | Professional & scientific | 2021 |
| Aurubis Finland Oy | Manufacturing | 2011 |
| Autek Oy | Professional & scientific | 2011 |
| Autio Tilat Oy | Real estate | 1977 |
| Auto- ja Venehuolto STK Oy | Other services | 2022 |
| Auto- ja konekorjaamo J. Marjakoski Oy | Other services | 2021 |
| Auto-Kirmola Oy | Manufacturing | 2003 |
| Auto-Nero oy | Other services | 2024 |
| Auto-Rantakallio Oy | Other services | 2010 |
| Auto-Termo Oy | Manufacturing | 2006 |
| Autohinaus Järvenpää & Virtanen, avoin yhtiö | Transport & logistics | 2002 |
| Autohuolto Mikkola Oy | Other services | 2025 |
| Autohuolto Rahtu Oy | Other services | 1990 |
| Autohuolto Tauno Mäkelä & Raili Kaurahalme | | 1986 |
| Autoilija Jaakko Niemi Oy | Transport & logistics | 2007 |
| Autokeskus Haapala Pori Oy | Other services | 2023 |
| Autokorjaamo Kivistö Oy | Other services | 2026 |
| Autokorjaamo Laine Oy | Other services | 2017 |
| Autokorjaamo Levomäki Oy | Other services | 2016 |
| Autokorjaamo Tiljander Kommandiittiyhtiö | Other services | 1977 |
| Automaalaamo A. Lahtinen Oy | Other services | 2019 |
| Automaalaamo J. Seppänen Oy | Other services | 1996 |
| Automaalaamo Reino Seppänen Kommandiittiyhtiö | Other services | 1989 |
| Automaattinen Tienaaminen Oy | Wholesale & retail | 2022 |
| Automyynti Lepistö oy | Wholesale & retail | 2024 |
| Automyynti Seppo Korhonen Oy | Wholesale & retail | 1998 |
| Autopeltikorjaamo Tapio Mattila Oy | Other services | 2011 |
| Autopesto Oy | Other services | 2006 |
| Autopesu Satafix Ky | Other services | 2016 |
| Autopesula Manninen Oy | Other services | 2022 |
| Autopinta Kiinteistöt Oy | Real estate | 2025 |
| Autotallit Oy Koivulantie 10-12 | Real estate | 1968 |
| Autotähti Oy | Wholesale & retail | 2017 |
| Autoyhtymä Koivula Ky | Transport & logistics | 2009 |
| Autoympyrä avoin yhtiö | Wholesale & retail | 1985 |
| Avanti Logistics Oy | Transport & logistics | 2022 |
| Avanto Partners Oy | Other services | 2020 |
| Avoin Yhtiö Eränaisten koirapalvelu | Other services | 2019 |
| Avoin Yhtiö JackRabbit Group | Professional & scientific | 2002 |
| Avoin yhtiö Hiussirkus | Other services | 2004 |
| Avoin yhtiö Marko ja Katri-Emilia Lång | Wholesale & retail | 2011 |
| Avoin yhtiö Nurmi ja Kallio | Hospitality | 2006 |
| Avoin yhtiö Vaajakari & Mäenpää | Hospitality | 2003 |
| AxPropria Oy | Financial services | 2026 |
| B&B Hair Design Oy | Other services | 2023 |
| Bfy OY | Administrative & support | 2021 |
| BMR Group Oy | Professional & scientific | 2022 |
| BMR Varastot Oy | Transport & logistics | 2020 |
| BTCRMX Group Oy | Wholesale & retail | 2026 |
| Baarine Oy | Hospitality | 2022 |
| Backyard Motors Oy | Other services | 2026 |
| Baggman Enterprise Oy | Financial services | 2026 |
| Balkenkreuz Capital Oy | Financial services | 2015 |
| Baltic Nuclear Consulting Group BNCG Oy | Professional & scientific | 2011 |
| Bankfield Oy | Information & communication | 2025 |
| Bar&co Pori Oy | Hospitality | 2010 |
| Bar57 Oy | Hospitality | 2014 |
| Basecamp Creative Oy | Professional & scientific | 2023 |
| Basofiili Oy | Health & social care | 2009 |
| BassoBurger Oy | Hospitality | 2011 |
| Bastu-Matti Oy | Professional & scientific | 1988 |
| Be Customer Smart Oy | Professional & scientific | 2017 |
| Be-Master Seppo Uusitalo Ky | Other services | 1989 |
| BeAn Solutions Oy | Information & communication | 2013 |
| BeBag Oy | Wholesale & retail | 2016 |
| Beacom Oy | Real estate | 2021 |
| Beamlaser Oy | Administrative & support | 2025 |
| Bear Valley Holding Ab | Financial services | 2020 |
| Bearfort Oy | Administrative & support | 1997 |
| Berry Superfos Pori Oy | Manufacturing | 1995 |
| BestHomes Oy | Real estate | 2019 |
| Besteam Oy | Manufacturing | 2006 |
| Betters Kiinteistöt Oy | Real estate | 2020 |
| Betters Oy | Construction | 2016 |
| Betters Yhtiöt Oy | Real estate | 2024 |
| BetweenHill Oy | Financial services | 2018 |
| BiHa Oy | Construction | 2010 |
| Bio Farmi Ky | Hospitality | 1985 |
| BioValue Oy | Professional & scientific | 2015 |
| Biocognitive Front Oy | Professional & scientific | 2026 |
| Biofacta Oy | Professional & scientific | 1991 |
| Birgit's Net Accounting Oy | Professional & scientific | 2010 |
| Bitradix Oy | Information & communication | 2017 |
| Björn & Borg Oy | Financial services | 2024 |
| Björneborg Estates Oy | Real estate | 2025 |
| Björneborg IPS Oy | Manufacturing | 2022 |
| Björneborgs svenska samskolas aktiebolag | Education | 1897 |
| Blind Chef's Oy | Hospitality | 2016 |
| Bloccare Oy | Information & communication | 2023 |
| Bloke Oy | Real estate | 2016 |
| Blomqvist Investment Oy | Real estate | 2019 |
| BoHa Services Oy | Administrative & support | 2023 |
| Bobergin Lohi, avoin yhtiö | Agriculture & fishing | 1985 |
| Bodoni Oy | Professional & scientific | 1997 |
| Bonapace Oy | Administrative & support | 2021 |
| Bondata Satakunta Oy | Administrative & support | 2018 |
| Bonnie blue Oy | Real estate | 2022 |