| Johnsen Drift AS | Construction | 2024 |
| Joma Eiendom AS | | 2025 |
| Jon Morten Halvorsen Invest AS | Other services | 2015 |
| Joppe AS | | 2024 |
| Joppe Hansen Dagligvare AS | Wholesale & retail | 2020 |
| Juel Johansens Bilruter Ans | Transport & logistics | 1992 |
| K. Danielsen Holding AS | Health & social care | 2015 |
| K.I Regnskap AS | Professional & scientific | 2009 |
| Kalnes Næringspark 5 AS | Real estate | 2024 |
| Kasiopea AS | Information & communication | 2021 |
| Kfdesign AS | Information & communication | 2019 |
| Kichi AS | Hospitality | 2021 |
| Kjøkkenprodukter AS | Wholesale & retail | 2025 |
| KR7 Holding AS | | 2019 |
| Kristiansen Mur Og Betongservice AS | Construction | 2016 |
| Krogstad Assuranse AS | Professional & scientific | 1986 |
| Krogstadfjorden Holding AS | | 2025 |
| Krogstadfjorden Marina AS | Manufacturing | 2025 |
| Kroppshelse AS | Education | 2025 |
| Kråkerøy Eiendom AS | Real estate | 2014 |
| Kulås Park Utvikling AS | Real estate | 2005 |
| Kvik Fredrikstad AS | Wholesale & retail | 2007 |
| L & L Holding AS | | 2025 |
| Lblyd AS | Arts & recreation | 2022 |
| Lease Consulting AS | Hospitality | 2010 |
| Lekehuset Østfold AS | Wholesale & retail | 2021 |
| LG Bygg & Eiendomsutvikling AS | Real estate | 2019 |
| Lge Holding AS | | 2025 |
| Life Kiropraktikk AS | Health & social care | 2012 |
| Lisleby Bil AS | Wholesale & retail | 2024 |
| Lkandersen Invest AS | | 2020 |
| LNL Da | Arts & recreation | 2024 |
| Lunds Klinikk AS | Health & social care | 2014 |
| M-Team AS | Construction | 2015 |
| M.I. Holding AS | | 2023 |
| Malecow AS | Wholesale & retail | 2020 |
| Malind Blomster AS | Wholesale & retail | 1999 |
| Manuell Terapi Klinikken Østfold AS | Health & social care | 2006 |
| Marin Holding AS | Real estate | 1997 |
| Marin Rør AS | Manufacturing | 2013 |
| Marinvernbruket AS | Professional & scientific | 2023 |
| Marksløjd AS | Wholesale & retail | 2013 |
| Marlan AS | Professional & scientific | 1989 |
| Merkotex Aktiebolag Nuf | Wholesale & retail | 2006 |
| Mge-Teknikk AS | Professional & scientific | 1999 |
| Michans Fot AS | Other services | 2020 |
| Minges Anleggsservice AS | Water & waste | 2012 |
| Minges Transportforretning Da | Transport & logistics | 2009 |
| MINIBUSS24-7 AS | Transport & logistics | 2006 |
| Mitt Deksel AS | | 2026 |
| MJ Consult AS | | 2021 |
| MLN Holding AS | Real estate | 2024 |
| Modell & Showbiz-Registeret Da | Professional & scientific | 1999 |
| Moderbolaget Holding AS | | 2022 |
| Mok Invest AS | | 2020 |
| Mortensen Capital AS | | 2025 |
| Mortensen Capital I AS | | 2025 |
| Mrs-Holding AS | | 2017 |
| Multilab Østfold AS | Professional & scientific | 2010 |
| Murmester Hansen Eiendom AS | Real estate | 2020 |
| Murmester Jan R Hansen & Sønn AS | Construction | 1999 |
| Murverk AS | Real estate | 2026 |
| Mvga AS | Wholesale & retail | 2022 |
| My Tran AS | Hospitality | 2010 |
| Myori Nordic AB Nuf | Wholesale & retail | 2004 |
| Martinsen Radio og TV Service ANS | Other services | 1988 |
| Møbelringen Fredrikstad AS | Wholesale & retail | 1959 |
| Møklegaard Print Shop AS | Manufacturing | 2001 |
| Naturo AS | Wholesale & retail | 1990 |
| Nautiluz Creation AS | Wholesale & retail | 2015 |
| Nctt Holmskau AS | | 2017 |
| Neckfocus AS | Professional & scientific | 2015 |
| Nedre Glomma Dyreklinikk AS | Professional & scientific | 2015 |
| Nedre Glomma Takst AS | Construction | 2016 |
| Nellys Fastfood AS | Hospitality | 2026 |
| Nes Forfatter Forening | Other services | 2013 |
| Nimbus Direct AS | Administrative & support | 2011 |
| Nimbus Gruppen AS | Professional & scientific | 2021 |
| NKV Invest AS | | 2024 |
| Norabi Språktjenester AS | Professional & scientific | 2020 |
| Norderhaugveien 15 AS | Real estate | 2026 |
| Nordic Crane Heavy Lift AB | Construction | 2009 |
| Nordic Defence AS | Information & communication | 2025 |
| Nordic Defence Systems AS | Information & communication | 2025 |
| Nordic Tents AS | Manufacturing | 2021 |
| Nordling Holding AS | | 2024 |
| Norduterom AS | Construction | 2026 |
| Norgesbad AS | Construction | 2025 |
| Nova-Bemanning AS | Administrative & support | 2026 |
| Nygaardsgata 48 AS | Real estate | 2026 |
| Nøstdal Holding AS | Construction | 2025 |
| Ohg 37 AS | Real estate | 2014 |
| Olafsen Invest AS | Real estate | 2016 |
| Omberg Eiendom AS | Real estate | 2021 |
| Omberg Invest AS | Financial services | 2021 |
| Op Mikalsen Transport AS | Transport & logistics | 2007 |
| Oredalshagen AS | Real estate | 2016 |
| Osflaten Hvitevarer Fredrikstad AS | Wholesale & retail | 2015 |
| P.A. Kristiansen AS | Professional & scientific | 2012 |
| Pedly Da | Arts & recreation | 2021 |