| Niinikangas & Berglund | Professional & scientific | 1980 |
| Niko Särkiniemi Ab | Health & social care | 2026 |
| Nikolai Steel Oy | Construction | 2007 |
| Niyom Thai Restaurant Oy | Hospitality | 2019 |
| Nocere Works Oy | Financial services | 2000 |
| NodeWorx Oy | Manufacturing | 2023 |
| Nodi growth services Ab | Professional & scientific | 2022 |
| Noesis Psykologi- ja psykoterapiapalvelut Oy | Health & social care | 2026 |
| NordWatt Oy | Energy | 2026 |
| Nordic Education Travel and Consult Oy | Administrative & support | 2025 |
| Nordic Electro Power Oy | Construction | 2016 |
| Nordic Energy Transition Ab | Construction | 2024 |
| Nordic Home Decor AB | Households | 2024 |
| Nordic Institute of Digital Innovations Ab | Education | 2018 |
| Nordic Insulation Partners Oy | Manufacturing | 2026 |
| Nordic Investment & Logistics OY | Financial services | 2013 |
| Nordic Live Productions Oy | Professional & scientific | 2013 |
| Nordic Living REY Oy | Real estate | 2020 |
| Nordic Solar Power Oy | Energy | 2022 |
| Nordic gastronomy Oy | Hospitality | 2025 |
| NordicTech Recycling Oy Ltd | Professional & scientific | 2022 |
| Nordics Energy Consultants Ab | Professional & scientific | 2018 |
| Nordlift Oy | Manufacturing | 2017 |
| Nordman Capital Oy Ab | Financial services | 2023 |
| Norrgårds disponent- och bokföring Ab | Real estate | 2023 |
| Norrskat Vattenandelslag | Water & waste | 2010 |
| Norrspel Ab | Wholesale & retail | 2026 |
| Norte Labs Oy | Professional & scientific | 2025 |
| North European Trading Co Netco Ky | Professional & scientific | 1983 |
| North Grove Consulting Ab Oy | Professional & scientific | 2020 |
| Northern Automation Oy | Manufacturing | 2005 |
| Northern Lights Holding Oy | Financial services | 2025 |
| Northgate Group Oy | Other services | 2021 |
| Northlux Oy | Professional & scientific | 2015 |
| Nortun OY | Information & communication | 2026 |
| Nova Group Oy | Information & communication | 2006 |
| Novafloor Oy | Wholesale & retail | 2007 |
| Novaviestintä Avoin Yhtiö | Professional & scientific | 1994 |
| Novixia Ab | Professional & scientific | 2025 |
| NstarN Oy Ab | Wholesale & retail | 2024 |
| Nuori Pääoma Oy | Manufacturing | 2024 |
| Nuri Heart Care Ab Oy | Health & social care | 2017 |
| Nuvantix Oy | Manufacturing | 2016 |
| NyAh Ekonomi Ab | Professional & scientific | 2023 |
| Nykarleby Vindpark Ab | Energy | 2012 |
| Nyplan Ab | Professional & scientific | 2024 |
| Närex Oy | Financial services | 1989 |
| Närpes Puls Ab | Real estate | 2012 |
| O & G Kustannus Ky | Information & communication | 1985 |
| O.U Capital Oy | Financial services | 2025 |
| O9 Consulting AB | Professional & scientific | 2014 |
| OCO Holdings Ab | Professional & scientific | 2026 |
| OD-Fastigheter Ab | Real estate | 2005 |
| OLPPU Oy | Real estate | 2025 |
| OV Invest Oy | Financial services | 2024 |
| OY EduRautamo AB | Education | 2023 |
| OY Niform AB | Manufacturing | 2015 |
| Oasis Finland Oy | Real estate | 2004 |
| Odin International Investment Oy Ltd | Professional & scientific | 2016 |
| Oftalmologi Lind Oy | Health & social care | 2021 |
| Oftamedi Oy | Health & social care | 2018 |
| Ogma Oy | Wholesale & retail | 2026 |
| Ohjelmatoimisto MeKaksi avoin yhtiö | Arts & recreation | 2020 |
| Oimaa Value Oy | Financial services | 2019 |
| Oivakaihdin Oy | Wholesale & retail | 1989 |
| Oki-Trans Oy Ab | Other services | 2012 |
| Olavi Collection Oy | Wholesale & retail | 2024 |
| Old World Productions Oy | Information & communication | 2025 |
| Oliver&Olivia Ab | Hospitality | 2021 |
| Olivetree avoin yhtiö | Hospitality | 2022 |
| Olympia-kioski Oy | Wholesale & retail | 1994 |
| Omatalliosake Oy | Real estate | 2011 |
| Ompelukoneliike Halonen Ky | Wholesale & retail | 1992 |
| One Earth & People Oy | Professional & scientific | 2026 |
| OneHitWonder Ab | Arts & recreation | 2022 |
| OneMecap Oy Ab | Information & communication | 2023 |
| Oneflow AB filial i Finland | Information & communication | 2021 |
| Onkilahden Lämpö Oy - Metvikens Värme Ab | Energy | 1965 |
| Onplane Ab Oy | Education | 2015 |
| Oomia Oy Ab | Hospitality | 2008 |
| Opak Oy | Financial services | 2018 |
| Opti-BESS Ab | Energy | 2026 |
| Opti-Pro Oy Ab | Wholesale & retail | 2025 |
| Opti-Substation Ab | Energy | 2026 |
| Optimointipalvelut Pirhonen Oy | Professional & scientific | 2024 |
| Optokoti Ab | Construction | 2026 |
| Oravais Trafik Ab - Oravaisten Liikenne Oy | Transport & logistics | 1950 |
| Orgonebox Oy | Professional & scientific | 2022 |
| Origo Epic Oy | Wholesale & retail | 2025 |
| Orre & Orre Öppetbolag | Wholesale & retail | 1993 |
| Osakeyhtiö Aterisystems Aktiebolag | Professional & scientific | 1979 |
| Oscon Rakennuspalvelu Oy | Construction | 2016 |
| Osteri Oy | Health & social care | 2021 |
| Ostro Business Oy Ab | Professional & scientific | 2012 |
| Ostro Real Invest II Oy | Real estate | 2025 |
| Ostro Real Invest Oy | Real estate | 2024 |
| OstroSafe Oy Ab | Administrative & support | 2012 |
| Ostrotrade Oy | Wholesale & retail | 2009 |
| Osuuskunta Hamnskärin pienvenesatama - Andelslag Hamnskär småbåtshamn | Arts & recreation | 2012 |
| Osuuskunta Kummelskärin Luontoasema Andelslaget | Administrative & support | 2014 |