| KB Drift AS | Professional & scientific | 2021 |
| Kean Invest AS | Financial services | 2014 |
| Kebab Pizza House 3 AS | Hospitality | 2020 |
| Kebab Zone AS | Hospitality | 2023 |
| Kebabhouse Sellebak AS | Hospitality | 2017 |
| Kebabhouse Sentrum AS | Hospitality | 2013 |
| Keibu Event AS | Hospitality | 2020 |
| Keiser Holdings AS | Wholesale & retail | 2020 |
| Kellox Trading AS | Wholesale & retail | 1966 |
| Key Fantasy Da | Professional & scientific | 2011 |
| Kgo Holding AS | | 2022 |
| Khli Holding AS | | 2019 |
| Kika Skjønnhet AS | Other services | 2021 |
| Kimrik Consulting AS | Information & communication | 2016 |
| King Event Limited Nuf | Information & communication | 2011 |
| Kiral AS | Information & communication | 2026 |
| Kirkegata 59 AS | Real estate | 2013 |
| Kiær Invest Eiendom II AS | Real estate | 2006 |
| KJ Marina Gressvik AS | Wholesale & retail | 2005 |
| Kjelaas Holding AS | Financial services | 2005 |
| Kjenes Eiendom & Invest AS | Wholesale & retail | 2019 |
| Kjetil's Trafikkskole AS | Education | 2025 |
| Kjgrotle Holding AS | | 2019 |
| Kjøkkengaarden AS | Wholesale & retail | 2008 |
| Kjøkkensenteret Østfold AS | Wholesale & retail | 1989 |
| Kjølholtåsen AS | Real estate | 2004 |
| Kjønig Holding AS | Real estate | 2010 |
| KK Bygg Kenneth Knædal AS | Construction | 2015 |
| Klarbygg AS | Construction | 2019 |
| Klart Nok AS | Education | 2026 |
| Klemsdal Holding AS | Real estate | 2005 |
| Klemsdal Invest AS | Real estate | 1949 |
| Klesforetaket AS | Wholesale & retail | 2024 |
| Klevmoen Eiendom AS | Real estate | 2024 |
| Klevmoen Invest AS | Real estate | 2024 |
| KM Eiendomsutvikling AS | Professional & scientific | 2014 |
| Knossos AS | Hospitality | 2015 |
| Kodemester AS | Information & communication | 2021 |
| Kohee AS | Professional & scientific | 2020 |
| Komplett Autosalg AS | Wholesale & retail | 2023 |
| Komplett Rør & Badstue AS | Construction | 2023 |
| Konmor AS | Professional & scientific | 2012 |
| Konsulentfirmaet Geir Kristoffersen AS | Real estate | 1990 |
| Konsulentpartner AS | Professional & scientific | 2024 |
| Kopling AS | Information & communication | 2017 |
| Kopperud Eiendom AS | Real estate | 1997 |
| Kopra AS | Wholesale & retail | 2024 |
| KR Kristiansen & Sønn AS | Real estate | 1972 |
| KR Leere Invest AS | Real estate | 2023 |
| Krabberødveien Landhandleri AS | Wholesale & retail | 2014 |
| Kreativ Omsorg AS | Health & social care | 2018 |
| KRN Holding Fredrikstad AS | Financial services | 2015 |
| Kråkerøy Rør AS | Construction | 1996 |
| Kråkerøyhallen AS | Real estate | 1971 |
| Kråkesølv Prosjekt AS | Real estate | 2021 |
| Kuben | | 1984 |
| Kultur Kåbbåy AS | Arts & recreation | 2021 |
| Kulturfangst AS | Administrative & support | 2016 |
| Kulturværste AS | Arts & recreation | 2005 |
| Kulturværste Produksjoner Da | Administrative & support | 2026 |
| Kvartalet Nygaardsgaten 28-30 AS | Real estate | 1970 |
| Kviq Innovation AS | | 2008 |
| Køl Fredrikstad AS | Hospitality | 2025 |
| La Granja AS | | 2023 |
| Laborel AS | Professional & scientific | 2012 |
| Ladestasjonen AS | Education | 1981 |
| Lagermoduler AS | Real estate | 2021 |
| Lagermoduler Tomteveien 43 AS | Real estate | 2021 |
| Lahellemoen Invest AS | Administrative & support | 2005 |
| Lakk-Spesialisten AS | Other services | 2004 |
| Lakk-Spesialisten Eiendom AS | Real estate | 2015 |
| Lakris Fredrikstad AS | Professional & scientific | 2005 |
| Lammenes Næringspark AS | | 2021 |
| Lande Senter AS | Real estate | 1997 |
| Langøyveien 16 AS | Real estate | 2012 |
| Lapemø Holding AS | Real estate | 2016 |
| Lareno AS | Real estate | 1989 |
| Larsen Prosjekter AS | Real estate | 2016 |
| Lavendula Ans | Wholesale & retail | 1990 |
| LC Tannteknikk AS | Health & social care | 2023 |
| Lea Invest AS | Wholesale & retail | 2003 |
| Learning Hub AS | Information & communication | 2020 |
| Lebri Holding AS | Hospitality | 2024 |
| Lechugal Eiendom AS | Real estate | 2019 |
| Ledproj AS | Wholesale & retail | 2021 |
| Leeres Båthotell 1 AS | Real estate | 2023 |
| Leeres Båthotell 3 AS | Real estate | 2023 |
| Leeres Motorsport AS | Wholesale & retail | 2023 |
| Lege Kathrine Hannestad AS | Health & social care | 2016 |
| Legeartis AS | Health & social care | 2015 |
| Legene I Nygaardsgata AS | Health & social care | 2016 |
| Legesenter Nygaardsgata AS | Health & social care | 2023 |
| Legionella Doktor'N Da | Professional & scientific | 2008 |
| Leisterud Byggkompetanse AS | Professional & scientific | 2011 |
| Lervikveien 26 AS | Real estate | 2009 |
| Lez Holding AS | | 2026 |
| Lia Eiendomsutvikling AS | Real estate | 2018 |
| Lie-Holt Holding AS | Professional & scientific | 2023 |
| Lie-Holt Invest AS | | 2021 |
| Life Dynamics AS | Health & social care | 2012 |