| Hammar & Wehkoja, öppet bolag | Wholesale & retail | 1998 |
| Happy Puppy Productions Ab | Information & communication | 2025 |
| Harma Electronics Oy | Professional & scientific | 2015 |
| Helléns Pälsfarm Ab | Agriculture & fishing | 1987 |
| Helsing Music Ab | Arts & recreation | 2015 |
| Henricson Ab | Professional & scientific | 1998 |
| Heplot Capital Ab | Financial services | 2020 |
| Hercules Fuels Ab | Professional & scientific | 2024 |
| Herrfors Nät-Verkko Oy Ab | Energy | 2007 |
| Herrmans Bike Components Oy | Manufacturing | 2019 |
| Hesa Capital Ab | Professional & scientific | 2025 |
| Hi-Line Products Kb | Construction | 2016 |
| HighHill Living Oy | Real estate | 2026 |
| Himalayan Flavours Ab | Manufacturing | 2023 |
| Hoang Tran Berries Ab | Wholesale & retail | 2026 |
| Hoitotaso Oy | Education | 2020 |
| Hoivanaika Oy | Health & social care | 2018 |
| Holm Trade Ab | Wholesale & retail | 2006 |
| Hommelholms Pälsfarm Ab | Agriculture & fishing | 1996 |
| Hopka Oy | Administrative & support | 2021 |
| Hägglunds Verkstad & Reservdelsaffär Ab | Wholesale & retail | 2007 |
| Hällans Vattenandelslag | Water & waste | 2002 |
| Hälsopraktik Natura Ab | Health & social care | 2015 |
| Håkan Södergård Ab | Agriculture & fishing | 1996 |
| Hölsömäen Turkis Oy | Agriculture & fishing | 1981 |
| Hötorgskiosken Ab | Hospitality | 2017 |
| ISS Finland Ab Oy | Manufacturing | 2026 |
| Ideal Solution Oy | Wholesale & retail | 2020 |
| In-Fa Jakobstad fastighet ab | Real estate | 1990 |
| InPress Finland OY | Information & communication | 2007 |
| IncludiCell Ab | Professional & scientific | 2015 |
| Ingenjörsbyrå Lärka Ab | Professional & scientific | 1987 |
| Ingves & Svanbäck Ab Oy | Transport & logistics | 2014 |
| Iniub Oy Ab | Wholesale & retail | 1997 |
| Inspio Ab | Construction | 2010 |
| Instant Solution Oy | Administrative & support | 2020 |
| International Berry Oy Ltd | Wholesale & retail | 2020 |
| Investomic Oy Ab | Professional & scientific | 2015 |
| Iris Jakobstad Ab Oy | Health & social care | 2018 |
| J & A Car Service Ab | Other services | 2017 |
| J. Koskinen Ky | Transport & logistics | 1992 |
| J. Ågren Transport Ab Oy | Transport & logistics | 2023 |
| J.Cederberg Ab | Wholesale & retail | 2021 |
| J.F.KEY Ab Oy | Professional & scientific | 2008 |
| JAS Invest Ab | Real estate | 2006 |
| JAVE Invest Oy | Real estate | 2023 |
| JB Nautical Oy | Manufacturing | 2022 |
| JEP Racing Oy | Construction | 2007 |
| JEPPIS Invest Oy Ab | Financial services | 2015 |
| JEPPIS Möbeltapetsering Ab | Other services | 2024 |
| JFO-Palvelut Oy | Financial services | 2021 |
| JHS Invest Ab | Financial services | 2010 |
| JHS Wood AB | Agriculture & fishing | 2026 |
| JK Hotels & Resorts Ab | Hospitality | 2001 |
| JK Hotels Service Ab | Administrative & support | 2001 |
| JKJ Fastigheter Ab | Real estate | 2005 |
| JKM Trading Ab | Construction | 2011 |
| JM Renovering Ab | Construction | 2026 |
| JMKSSE Invest Ab | Manufacturing | 2018 |
| JMM Asset Mgt Oy | Financial services | 2024 |
| JMM-e Oy | Professional & scientific | 2024 |
| JMR-Invest Ab | Real estate | 2021 |
| JMS Solutions Ab Oy | Other services | 2022 |
| JOWACON Oy Ab | Real estate | 2012 |
| JP-Omas avoin yhtiö | Hospitality | 1991 |
| JS Fastighetsservice Ab Oy | Construction | 2005 |
| JS-Shine öppet bolag | Other services | 2023 |
| JSCon Ab | Information & communication | 2023 |
| Jake Rakennus Oy | Construction | 2003 |
| Jako Invest Ab Oy | Real estate | 2007 |
| Jakob Garden Oy | Arts & recreation | 2008 |
| Jakob-Team Oy | Financial services | 2003 |
| Jakobstads Bilmålarservice Ab Oy | Other services | 1984 |
| Jakobstads Bilskrot Ab | Wholesale & retail | 2005 |
| Jakobstads Bogser Ab - Pietarsaaren Hinaus Oy | Real estate | 1979 |
| Jakobstads Budservice Ab | Transport & logistics | 2008 |
| Jakobstads Disponentservice Ab - Pietarsaaren Isännöintipalvelu Oy | Real estate | 2008 |
| Jakobstads Energi Ab | Energy | 2014 |
| Jakobstads Fastighetsförmedling Ab | Real estate | 2025 |
| Jakobstads Fitness Club Oy Ab | Arts & recreation | 1991 |
| Jakobstads Företagsfastigheter Ab | Real estate | 1960 |
| Jakobstads Försäljningskontor, Elke, öppet bolag | Wholesale & retail | 1988 |
| Jakobstads Gamla Hamn Ab - Pietarsaaren Vanha Satama Oy | Transport & logistics | 1988 |
| Jakobstads Hamn Ab | Transport & logistics | 2014 |
| Jakobstads Kafferosteri Ab | Manufacturing | 2025 |
| Jakobstads Kanalkiosken, avoin yhtiö | Wholesale & retail | 1988 |
| Jakobstads Konsertsal Ab | Arts & recreation | 2011 |
| Jakobstads Rättstjänst Ab | Professional & scientific | 1956 |
| Jakobstads Saigon Bar Restaurang öppet bolag | Hospitality | 2011 |
| Jakobstads Torgparkering Ab - Pietarsaaren Toripysäköinti Oy | Transport & logistics | 2015 |
| Jakobstads Ulataxi Andelslag - Pietarsaaren Ulataxi Osuuskunta | Information & communication | 1973 |
| Jakobstads-Bilfrakt Ab | Transport & logistics | 1961 |
| Jakobstadsnejdens Telefon Ab | Information & communication | 1915 |
| Jank-Foto Kb | Professional & scientific | 1989 |
| Jantek Oy | Construction | 2025 |
| Jarimisa Oy | Wholesale & retail | 1990 |
| Jasomar Oy | Real estate | 1996 |
| Jbb Fastighetsförvaltning Ab | Professional & scientific | 1992 |
| Jenmedi Oy | Health & social care | 2019 |
| Jennan Palvelut Oy | Administrative & support | 2020 |