| Atmos Helsinki Oy | Other services | 2021 |
| Atmos Oy | Health & social care | 2008 |
| Atmotics Oy | Information & communication | 2022 |
| Atol Investment Oy | Financial services | 2026 |
| Atomed Oy | Health & social care | 2020 |
| Atomi Labs Oy | Information & communication | 2026 |
| Atomic Spa Studios Oy | Arts & recreation | 2011 |
| Atomic Swing Oy | Professional & scientific | 2010 |
| Atomica Invest Oy | Financial services | 2021 |
| Atomidata Oy | Information & communication | 2023 |
| Atomirotta Oy | Arts & recreation | 2015 |
| Atomitie Music Oy | Arts & recreation | 2025 |
| Atomus Invest Oy | Professional & scientific | 2017 |
| Aton Oy | Administrative & support | 1989 |
| Atonic Studios Oy | Information & communication | 2017 |
| Atono Invest Oy | Financial services | 2020 |
| Atopää Oy | Wholesale & retail | 2022 |
| Atos IT Solutions and Services Oy | Information & communication | 2010 |
| Atradius Crédito y Caución S.A. de Seguros y Reaseguros, sivuliike Suomessa | Financial services | 2016 |
| Atrap Oy | Wholesale & retail | 2017 |
| Atresia Oy | Financial services | 2006 |
| Atrium Media Oy | Information & communication | 2025 |
| Atrocious Ventures Oy | Financial services | 2023 |
| Atsalea Software Oy | Information & communication | 2013 |
| Atsipoppaa Oy | Hospitality | 2025 |
| Atsoft Oy Mäkinen | Information & communication | 1988 |
| Attacco Oy | Arts & recreation | 2008 |
| Attack Point Consulting Oy | Professional & scientific | 2013 |
| Attaren Oy | Wholesale & retail | 2019 |
| AtteBee Oy | Professional & scientific | 2020 |
| Attelier Oy | Wholesale & retail | 2026 |
| Attencion Oy | Professional & scientific | 2017 |
| Attendo 247 Oy | Health & social care | 2014 |
| Attendo Aapelikoti Oy | Health & social care | 1999 |
| Attendo Askelkodit Oy | Health & social care | 1998 |
| Attendo Aurinkopuisto Oy | Health & social care | 1997 |
| Attendo DF-Care Oy | Professional & scientific | 2008 |
| Attendo Donum Oy | Health & social care | 2004 |
| Attendo Eevakoti Oy | Health & social care | 2005 |
| Attendo Enckelinpuisto Oy | Health & social care | 2014 |
| Attendo Etelä-Suomen Kotihoito Oy | Real estate | 2017 |
| Attendo Friitalan Palvelukoti Oy | Health & social care | 2008 |
| Attendo GG-Hoiva Oy | Health & social care | 2007 |
| Attendo Give Oy Hoivakoti | Health & social care | 2005 |
| Attendo Hakami Oy | Health & social care | 1996 |
| Attendo Helinä Oy | Health & social care | 2005 |
| Attendo Helmakodit Oy | Health & social care | 1991 |
| Attendo Hoitokoti Apilaniitty Oy | Health & social care | 2006 |
| Attendo Hoivakoti Misteli Oy | Health & social care | 2004 |
| Attendo Huhtihovi Oy | Health & social care | 2017 |
| Attendo Huurmanni Oy | Health & social care | 2010 |
| Attendo Ikihyvä Oy | Health & social care | 2008 |
| Attendo Iltatuuli Oy | Health & social care | 2010 |
| Attendo Imatran Palvelukoti Oy | Health & social care | 1993 |
| Attendo Itä-Suomen Kotihoito Oy | Health & social care | 1993 |
| Attendo Jelppiskoti Oy | Health & social care | 2008 |
| Attendo Joen Hoiva Oy | Health & social care | 2013 |
| Attendo Joenranta Oy | Health & social care | 2000 |
| Attendo Jokikoto Oy | Health & social care | 2008 |
| Attendo Juankosken Hoiva Oy | Health & social care | 2009 |
| Attendo Juuan Hoiva Oy | Health & social care | 2000 |
| Attendo Kaijankoti Oy | Health & social care | 1997 |
| Attendo Kanervikkola Oy | Health & social care | 2003 |
| Attendo Kellokas Oy | Health & social care | 2006 |
| Attendo Kotiplus Oy | Health & social care | 1989 |
| Attendo Kotiruhtinas Oy | Health & social care | 2016 |
| Attendo Kruunankulma Oy | Health & social care | 2002 |
| Attendo Kultaharju Oy | Health & social care | 2006 |
| Attendo Kultarinki Hoivapalvelut Oy | Health & social care | 2008 |
| Attendo Kuntoutumiskoti Harjula Oy | Health & social care | 1996 |
| Attendo Larosette Oy | Health & social care | 1999 |
| Attendo Liedon Helmi Oy | Health & social care | 1999 |
| Attendo Liisankoti Oy | Health & social care | 1996 |
| Attendo Lilla Ro Oy | Health & social care | 2000 |
| Attendo Luotolahden Kuntoutus Oy | Health & social care | 1983 |
| Attendo Majakka Oy | Health & social care | 1993 |
| Attendo Marian Kartano Oy | Health & social care | 1998 |
| Attendo Mental Oy | Health & social care | 2005 |
| Attendo Meri-Lappi Oy | Health & social care | 2008 |
| Attendo Mi-Hoiva Oy | Health & social care | 1989 |
| Attendo Mikkelin Palvelukoti Oy | Health & social care | 1985 |
| Attendo Mäntytuuli Oy | Health & social care | 2007 |
| Attendo Mäntän Palvelukoti Oy | Health & social care | 2000 |
| Attendo Napapiirin Hoiva Oy | Health & social care | 2010 |
| Attendo Neliapila Oy | Health & social care | 2000 |
| Attendo Nurmeksen Hoiva Oy | Health & social care | 2005 |
| Attendo Omena Oy | Health & social care | 2007 |
| Attendo Onnentäyttymys Oy | Health & social care | 2008 |
| Attendo Orimattila Oy | Health & social care | 1990 |
| Attendo Oy | Health & social care | 2002 |
| Attendo Palvelukoti Auringonrusko Oy | Health & social care | 2006 |
| Attendo Palvelukoti Rauha Oy | Health & social care | 2005 |
| Attendo Palvelukoti Sinivakka Oy | Health & social care | 2005 |
| Attendo Palvelukoti Väisänen Oy | Health & social care | 1992 |
| Attendo Pekkalakoti Oy | Health & social care | 1997 |
| Attendo Pielaveden Palvelukoti Oy | Health & social care | 1991 |
| Attendo Piritta Oy | Health & social care | 1993 |
| Attendo Puruveden Helmi Oy | Health & social care | 1991 |
| Attendo Raahen Palvelukoti Oy | Health & social care | 1996 |
| Attendo Saviria Oy | Health & social care | 2021 |