| 1496 Saara Aho Oy | Wholesale & retail | 2016 |
| 3D Ilme Juha Lihr Oy | Professional & scientific | 2011 |
| 52 Degrees N Oy | Administrative & support | 2021 |
| 5min app oy | Information & communication | 2025 |
| 64North Oy | Information & communication | 2026 |
| 73Health Oy | Information & communication | 2022 |
| 88 North Assets Oy | Real estate | 2024 |
| A&M Services Oy | Transport & logistics | 2024 |
| A&P Metsä Oy | Agriculture & fishing | 2024 |
| A-Luokan Varaosatukku Kajaani Oy | Wholesale & retail | 2017 |
| A. Kaakinen Oy | Financial services | 1933 |
| AIM Yhdessä Oy | Financial services | 2024 |
| AJ-Myynti Oy | Wholesale & retail | 2013 |
| AJE Manninen Ky | Wholesale & retail | 2021 |
| AJH Interior furniture Oy | Wholesale & retail | 2006 |
| AKE-GEARS Oy | Manufacturing | 2008 |
| AKKE Finlandia Oy | Wholesale & retail | 2010 |
| AM Beauty Oy | Wholesale & retail | 2018 |
| AP-Hyvärinen Autokorjaamo Oy | Other services | 2015 |
| ATTA Investing Oy | Financial services | 2023 |
| Atta Nordic Transfers OY | Transport & logistics | 2020 |
| AVH-Consulting Oy | Professional & scientific | 2024 |
| AVP Sijoitus Oy | Administrative & support | 2023 |
| Aavacare Oy | Wholesale & retail | 1999 |
| Acema Oy | Information & communication | 2026 |
| Ahappa Oy | Wholesale & retail | 1995 |
| Ahonen Design Oy | Professional & scientific | 2017 |
| Aija Roininen Ky | Hospitality | 1987 |
| Air Systems Kajaani avoin yhtiö | Administrative & support | 2006 |
| Aito Food Company Oy | Hospitality | 2019 |
| Aito Milano Oy | Hospitality | 2025 |
| Aitokaluste Oy | Manufacturing | 2013 |
| Aitta-Kiinteistöt Oy | Real estate | 2019 |
| Akkukauppa Kemppainen Oy | Wholesale & retail | 1968 |
| Alkumetsä Oy | Agriculture & fishing | 2021 |
| Alueurakointi Poutiainen Oy | Administrative & support | 2013 |
| Anbao Oy | Hospitality | 2025 |
| Anita Kovalainen Import Oy | Other services | 1996 |
| Anne Kyllönen Oy | Professional & scientific | 2019 |
| Annotar Oy | Information & communication | 2025 |
| Anorak Society Oy | Hospitality | 2015 |
| Apicis Oy | Construction | 1986 |
| Applirent Oy | Information & communication | 2017 |
| Apuri Tuote Oy | Manufacturing | 2006 |
| Arcal Group Oy | Professional & scientific | 2024 |
| Arctic Bio Valley Oy | Wholesale & retail | 2020 |
| Arctic Lake Experience Kainuu Oy | Hospitality | 2020 |
| Arctic nightlife Oy | Hospitality | 2026 |
| Arffman Finland Oy | Education | 2006 |
| Ari Kananen Consulting Oy | Education | 2023 |
| Ari Partasen kauppapuutarha Ky | Agriculture & fishing | 1990 |
| Arithme Oy | Financial services | 2015 |
| Arja ja Eero Juntunen Oy | Mining & quarrying | 1995 |
| Arjen Ilona Oy | Health & social care | 2025 |
| Arkkitehtitoimisto Johansson Ky | Professional & scientific | 1982 |
| Arkotekniikka Ky | Manufacturing | 1990 |
| Arstec Oy | Wholesale & retail | 2023 |
| Ase- ja Optiikkahuolto H. Korhonen Oy | Wholesale & retail | 2013 |
| Asennus-Sissi Oy | Construction | 2005 |
| Asianajotoimisto Antti Kejo Ky | Professional & scientific | 1991 |
| Asianajotoimisto Jukka Suhonen Ky | Professional & scientific | 2004 |
| Asianajotoimisto Kai Rissanen Oy | Professional & scientific | 2012 |
| Asianajotoimisto Kejo Oy | Professional & scientific | 2014 |
| Asianajotoimisto Mikael Knuuti Ky | Professional & scientific | 1985 |
| Asiantuntijapalvelut Anssi Heikkinen Ky | Professional & scientific | 2023 |
| Asina Family Oy | Transport & logistics | 2019 |
| Astu-Sisään kenkäkauppa Oy | Wholesale & retail | 2007 |
| Auhojärven majoitus Oy | Hospitality | 2025 |
| Auma-Talot Oy | Construction | 2015 |
| Aurinko Store Oy | Wholesale & retail | 2021 |
| Aurinkoaika I Oy | Real estate | 1990 |
| Aurinkorumpu Oy | Wholesale & retail | 2022 |
| Aution Puutyöhallit Oy | Manufacturing | 1974 |
| Auto Åman Oy | Wholesale & retail | 2020 |
| Auto-Kaja avoin yhtiö | Wholesale & retail | 2013 |
| Auto-Salomo Oy | Financial services | 1987 |
| AutoSalar Oy | Wholesale & retail | 2021 |
| Autohuolto Kaijala & Kuittinen Oy | Other services | 2002 |
| Autohuolto SaKe avoin yhtiö | Other services | 2014 |
| Autohuolto Tolonen Oy | Other services | 2013 |
| Autokorjaamo Karppinen & Åman Oy | Other services | 2005 |
| Automaalaamo JP-Paint Ky | Other services | 2012 |
| Automaalaamo Matin Fiksaus Oy | Other services | 1988 |
| Automyynti Witikka Oy | Wholesale & retail | 2006 |
| Automyynti-Kjn Oy | Wholesale & retail | 2021 |
| Autopalvelu Hyvärinen Oy | Other services | 1982 |
| Autoreal Oy | Wholesale & retail | 2012 |
| Autosähkökorjaamo Ässä Oy | Other services | 2017 |
| Autotema Ky Kajaani | Other services | 1990 |
| Autovälitys Peltoniemi Oy | Wholesale & retail | 2020 |
| Aveone Oy | Wholesale & retail | 2015 |
| Avoin yhtiö Eläinplaneetta | Wholesale & retail | 2000 |
| Avoin yhtiö Kajaanin Lounaspalvelu | | 1993 |
| Avoin yhtiö Törmi & Törmi | Health & social care | 2012 |
| B&E Rakennuttajat Oy | Real estate | 2020 |
| Balance Kajaani OY | Arts & recreation | 2009 |
| BAZIA-SALAMA Oy | Professional & scientific | 2024 |
| BTK Rakennus Oy | Construction | 2026 |
| Backyard Holding Oy | Financial services | 2024 |
| Ballmec Oy | Professional & scientific | 2011 |