| Osakeyhtiö Birger Hallman | Real estate | 2009 |
| Osakeyhtiö Hallman | Financial services | 1897 |
| Osakeyhtiö Ropo poikineen | Financial services | 2020 |
| Osaset.com Oy | Wholesale & retail | 2004 |
| Oskor Oy | Hospitality | 2015 |
| Oslo Palvelut Oy | Administrative & support | 2021 |
| Osteopathic Energy Oy | Health & social care | 2017 |
| Osto- ja myyntiliike Vilin valinta Ky | Wholesale & retail | 2013 |
| Osuma Group Oy | Professional & scientific | 2019 |
| Osuma Henkilöstöpalvelut II Oy | Other services | 2025 |
| Osuma Henkilöstöpalvelut III Oy | Other services | 2025 |
| Osuma Henkilöstöpalvelut IV Oy | Other services | 2025 |
| Osuma Henkilöstöpalvelut Oy | Other services | 2016 |
| Osuma Henkilöstöpalvelut V Oy | Other services | 2025 |
| Osuma Henkilöstöpalvelut VI Oy | Other services | 2025 |
| Osuma Turvallisuuspalvelut Oy | Other services | 2020 |
| Osuuskauppa PeeÄssä | Wholesale & retail | 1991 |
| Osuuskunta Konsti X | Professional & scientific | 1997 |
| Osuuskunta Kuopion Avainosaajat | Professional & scientific | 1995 |
| Osuuskunta Sataman Tarmo | Wholesale & retail | 2012 |
| Osuuskunta Suomen taide ja taidekokoelmat | Information & communication | 2014 |
| Osuuskunta Ääni & Apu | Health & social care | 2003 |
| Otia Invest Oy | Construction | 2023 |
| Otomed avoin yhtiö | Health & social care | 2004 |
| Otso Protection Oy | Manufacturing | 2026 |
| Oulun Performance Institute Oy | Health & social care | 1994 |
| Ouwau Design & Productions Oy | Professional & scientific | 2021 |
| OviPro Oy | Construction | 2015 |
| Owela Oy | Information & communication | 2015 |
| Oy Arroy Ab | Wholesale & retail | 1989 |
| Oy Berry Market Finland Ltd | Wholesale & retail | 2000 |
| Oy CargoMate Ltd | Professional & scientific | 2019 |
| Oy Carlson | Wholesale & retail | 1900 |
| Oy Carno Impex Ltd | Wholesale & retail | 2000 |
| Oy Caso Import | Wholesale & retail | 1962 |
| Oy Diagnostic Devices Development - DDD | Manufacturing | 2007 |
| Oy Elcab Ab | Other services | 1997 |
| Oy Elkamer Ab | Professional & scientific | 1997 |
| Oy Epuro Ab | Real estate | 1994 |
| Oy Finmonte Ab | Construction | 1994 |
| Oy Fintrade Services LTD | Manufacturing | 1989 |
| Oy Finvaleur Ab | Wholesale & retail | 1994 |
| Oy Global Sales Point Ltd | Wholesale & retail | 2020 |
| Oy Gust. Ranin | Manufacturing | 1919 |
| Oy H & M Rouvinen Consulting Ltd | Professional & scientific | 1998 |
| Oy Hugo Korhonen Creative Ltd | Education | 2025 |
| Oy KK-Group Ltd | Financial services | 1987 |
| Oy Kiti-Trans Ab | Transport & logistics | 2020 |
| Oy Leader Chemicals Ab | Wholesale & retail | 2013 |
| Oy MUOTO-STEAM Ltd | Manufacturing | 2006 |
| Oy Mehustaja Finland Ab | Manufacturing | 2009 |
| Oy Meninx Ltd | Professional & scientific | 1995 |
| Oy National Chemicals Ab | Wholesale & retail | 2011 |
| Oy Polon Ab | Professional & scientific | 1973 |
| Oy Sauloner Ltd | Professional & scientific | 2008 |
| Oy Scanria Ab | Information & communication | 1994 |
| Oy Scantarp Ab | Manufacturing | 2021 |
| Oy Shinovent Ltd | Information & communication | 2017 |
| Oy Swiss Group Ab | Financial services | 2016 |
| Oy Trading Rengas Ab | Wholesale & retail | 1993 |
| Oy Tsuyako Ltd | Other services | 2020 |
| Oy Turo Tailor Ab | Manufacturing | 1997 |
| Oy Valand Ab | Wholesale & retail | 1989 |
| Oy Wellamonkatu 11 | Real estate | 1922 |
| Oz Medication Technology Oy | Information & communication | 2019 |
| Ozirc Solutions Oy | Information & communication | 2021 |
| P Asian Market Oy | Wholesale & retail | 2026 |
| P Kananen Oy | Transport & logistics | 2023 |
| P&P Autohuolto Ky | Other services | 2013 |
| P&P Kattohuolto Oy | Administrative & support | 2015 |
| P-S Kalavesienhoito oy | Agriculture & fishing | 2013 |
| P.A team Oy | Administrative & support | 2023 |
| P.K. Cleaning Ky | Administrative & support | 2009 |
| P.Piuha Oy | Construction | 2019 |
| PAL Trading & Logistics Oy | Wholesale & retail | 2021 |
| PC-Soft kommandiittiyhtiö | Information & communication | 1984 |
| PEO Ravintolat Oy | Hospitality | 2014 |
| Perhekoti Puijo OY | Health & social care | 2003 |
| PETRIFUN Oy | Wholesale & retail | 1973 |
| PG. Vision Oy | Financial services | 2023 |
| PIAZZA ITALIA Oy | Hospitality | 2021 |
| PJM Meklarit Oy | Financial services | 2026 |
| PJN-Kapital Oy | Real estate | 2024 |
| PK Caravanpalvelut Oy | Other services | 2025 |
| PK Product Oy | Wholesale & retail | 1990 |
| PK Varastot avoin yhtiö | Other services | 1997 |
| PKP Group Oy | Wholesale & retail | 2013 |
| PKR-Markkinointi Oy | Wholesale & retail | 2010 |
| Plastic Surgery Center Group OY | Health & social care | 2022 |
| PLuS Nutrition Oy | Health & social care | 2025 |
| Pma Explotech OY | Wholesale & retail | 2007 |
| POK Group Oy | Manufacturing | 1979 |
| PP Detailing avoin yhtiö | Other services | 2018 |
| PPH-kiinteistöinsinöörit Oy | Professional & scientific | 2017 |
| Pr-Kaluste Ja Saneeraus OY | Construction | 2007 |
| PRAP KY (Puijon Rakennus Asennus Palvelu) | Construction | 2008 |
| Priimailma OY | Construction | 2018 |
| PRO Tilikirjat Oy | Administrative & support | 2025 |
| PS Kiinteistösijoitus Oy | Real estate | 2026 |
| PS-Marketing Ky | Wholesale & retail | 2005 |