| Oy Hammarén & Co Ab | Financial services | 1984 |
| Oy Hammas-Väisänen Ab | Health & social care | 1997 |
| Oy Hamnkopplan Ab | Real estate | 2007 |
| Oy Hanna Shipping Ltd | Transport & logistics | 1988 |
| Oy Hansa-Astra Ab | Professional & scientific | 1993 |
| Oy Hansamade Ab | Arts & recreation | 1992 |
| Oy Hansard Ltd | Wholesale & retail | 1988 |
| Oy Hapag-Lloyd Finland Ab | Transport & logistics | 1979 |
| Oy Happi Partners Ab | Professional & scientific | 2020 |
| Oy Hartwall Ab | Manufacturing | 1908 |
| Oy Hassanein Ltd | Wholesale & retail | 2008 |
| Oy Heartagram Ltd | Arts & recreation | 2000 |
| Oy Hedengren Ab | Financial services | 1918 |
| Oy Hedengren Capital Ab | Professional & scientific | 2023 |
| Oy Hedengren Security Ab | Wholesale & retail | 1990 |
| Oy Hedix Ab Ltd | Professional & scientific | 2004 |
| Oy Hedtec Ab | Wholesale & retail | 1998 |
| Oy Helena Haapio & Co | Professional & scientific | 1985 |
| Oy Helena Sandman Ab | Professional & scientific | 1997 |
| Oy Heli Engdahl Ab | Administrative & support | 2024 |
| Oy Helibertel-Invest Ab | Administrative & support | 1995 |
| Oy Hellström Capital Ab | Financial services | 2022 |
| Oy Hellää Hoivaa - Varsam Vård Ab | Health & social care | 2021 |
| Oy Helplab Ab | Professional & scientific | 2021 |
| Oy Helsingin Auto-Bil Ab | Wholesale & retail | 2016 |
| Oy Helsingin Kromipainoteollisuus Helsingfors Industri Ab Cromtryck | Manufacturing | 1993 |
| Oy Helsingin Luisteluareena - Helsingfors Skridskoarena Ab | Arts & recreation | 2017 |
| Oy Helsingin Nuori Herra Ltd | Hospitality | 1997 |
| Oy Helsingin Pontikkatehdas Ab | Manufacturing | 2022 |
| Oy Helsingin Rakennesaumaus | Construction | 1987 |
| Oy Helsingin Yhteiskoulu ja Reaalilukio | Education | 1924 |
| Oy Helsingin tietotekniikkapalvelut Ab | Wholesale & retail | 2007 |
| Oy Helsinki Chartering Ab | Transport & logistics | 1987 |
| Oy Helsinki Ear Institute Inc. | Health & social care | 1996 |
| Oy Helsinki Homemade Ab | Manufacturing | 2018 |
| Oy Hennet Ltd | Wholesale & retail | 1992 |
| Oy Henrik's Jewelry Ltd | Information & communication | 1990 |
| Oy Heritax Ab | Professional & scientific | 2025 |
| Oy Hermitage Ab | Financial services | 1990 |
| Oy Hiccum Ab | Information & communication | 1995 |
| Oy High Touch Ab | Financial services | 1990 |
| Oy Hiiskula Ab | Financial services | 1984 |
| Oy Hill SMI Ab | Financial services | 2024 |
| Oy Hiusmuotoilu Point PH | Other services | 1995 |
| Oy Hobel Ab | Real estate | 1991 |
| Oy Holding Company Ab | Financial services | 1974 |
| Oy Home Dining Finland Ab | Administrative & support | 2014 |
| Oy Home Harmony Ab | Professional & scientific | 2001 |
| Oy HomeRef LKV | Real estate | 2023 |
| Oy Homekit Ab | Wholesale & retail | 2011 |
| Oy HooVeeSec Ab | Information & communication | 2015 |
| Oy Horcon Ab | Professional & scientific | 1989 |
| Oy Horme Ab | Health & social care | 2011 |
| Oy Hospitality and Retail Systems Finland | Wholesale & retail | 2018 |
| Oy Hotelli Puffeli Ab | Hospitality | 2003 |
| Oy House of North Ltd. | Professional & scientific | 2017 |
| Oy House of Sandwiches Finland Ltd | Hospitality | 1995 |
| Oy Hude Ab | Real estate | 1989 |
| Oy Husön Arena Ab | Education | 2010 |
| Oy Husön Ratsastuskeskus Ab | Education | 1987 |
| Oy Hygsight Ltd | Professional & scientific | 2025 |
| Oy Hypolatur Holding Ab | Professional & scientific | 2011 |
| Oy Hytönen & Hytönen Ab | Administrative & support | 2011 |
| Oy Häggvik Ab | Real estate | 1973 |
| Oy Högfors-Trading Ab | Financial services | 2017 |
| Oy IBM Finland Ab | Information & communication | 1937 |
| Oy ICS Intelligent Control Systems Ltd | Professional & scientific | 1994 |
| Oy IKB Trading Ltd. | Financial services | 1986 |
| Oy ITCC Ltd International Trade Centre Corporation | Wholesale & retail | 1990 |
| Oy Iber-Nordica Ab | Professional & scientific | 1993 |
| Oy Ideapiiri Ab | Real estate | 1991 |
| Oy Ideatank Ltd | Professional & scientific | 2020 |
| Oy Identcard Ab | Information & communication | 2003 |
| Oy Ikkunanpuhdistusliike Kaleva Ab | Administrative & support | 1965 |
| Oy Ilmakos Ab | Construction | 2015 |
| Oy Immoman Ltd | Professional & scientific | 1990 |
| Oy Implantona Finland Ltd | Wholesale & retail | 1994 |
| Oy Inbux Ab | Wholesale & retail | 1996 |
| Oy Indicia Ab | Professional & scientific | 2024 |
| Oy Infowell Ab | Professional & scientific | 1990 |
| Oy Inga Pengar Ab | Professional & scientific | 2023 |
| Oy Ingenjörsbyrån Pluton Ab | Wholesale & retail | 1956 |
| Oy Inreviso Ab | Professional & scientific | 1984 |
| Oy Insinööritoimisto Lars Rundberg Ab | Manufacturing | 1985 |
| Oy Inspirit Consulting Inc. | Professional & scientific | 1997 |
| Oy Integritatium Ab | Administrative & support | 1985 |
| Oy Interco Ab | Wholesale & retail | 1950 |
| Oy Interfina Ab | Professional & scientific | 1994 |
| Oy International FinnEke Shipping Ltd | Financial services | 2006 |
| Oy International Ingen Ab | Financial services | 1997 |
| Oy International Multiple Industry Ltd | Information & communication | 1990 |
| Oy International Thinking Organization Ltd | Financial services | 1989 |
| Oy Intiakeskus/India Centre Ab | Administrative & support | 1976 |
| Oy Invenio Ab | Professional & scientific | 2006 |
| Oy Inventiainvest Ab | Financial services | 1988 |
| Oy Inverness Ab | Professional & scientific | 1977 |
| Oy Investcon Ab | Professional & scientific | 1981 |
| Oy Investeringsföreningen Kamraterna Ab | Financial services | 2020 |
| Oy Investsum Ab | Financial services | 1985 |
| Oy Iron Ventures Ab | Financial services | 2026 |