| Kjeveortoped Schultz AS | Health & social care | 2022 |
| Klartjern AS | | 2017 |
| Klippehjørnet Da | Other services | 1995 |
| Kmea Holding AS | Education | 2024 |
| Knivsøparken AS | Real estate | 2013 |
| Knobel AS | Real estate | 2013 |
| Knobel Holding AS | | 2017 |
| KNS Eiendom AS | Real estate | 2016 |
| Kocu Eiendom AS | Hospitality | 2016 |
| Kocu Invest AS | Hospitality | 2018 |
| Kodebruket AS | Information & communication | 2026 |
| Kokkekollektivet Halden AS | Hospitality | 2017 |
| Kollen Holding AS | Financial services | 2013 |
| Kolås Eftf AS | Construction | 1985 |
| Kombin Økonomi & Ledelse AS | Professional & scientific | 2026 |
| Kompenda AS | Professional & scientific | 2023 |
| Kompenda Norge AS | Information & communication | 2022 |
| Kongegården Eiendom AS | Real estate | 2001 |
| Kongshallene AS | Hospitality | 2011 |
| Kontorsenteret Østfold AS | Wholesale & retail | 2003 |
| Kopper Og Blikkenslagermester Terje W Granstrøm AS | Construction | 2001 |
| Kosterfjord AS | | 2017 |
| KPP Holding AS | Information & communication | 2023 |
| KPT Holding AS | | 2025 |
| Krankroken AS | Wholesale & retail | 2015 |
| Kratos Holding AS | | 2017 |
| Kreere AS | Professional & scientific | 2007 |
| Krieli AS | | 2023 |
| Kristian Stenrød Holding AS | | 2025 |
| Krogh Antikk & Vintage AS | Wholesale & retail | 2016 |
| Krogs Pizza Og Grill AS | Hospitality | 2024 |
| Krosvik Invest AS | | 2026 |
| Kruse Investeringer AS | | 2024 |
| KS Construction | Professional & scientific | 2008 |
| Kulturinvest Halden AS | Real estate | 2014 |
| Kulås Terrasse 6 Eiendom AS | Real estate | 2024 |
| Kurant Halden AS | | 2022 |
| Kurant Investering AS | | 1986 |
| Kursexperten AS | Education | 2022 |
| Kvaro AS | Professional & scientific | 2024 |
| Kvitfjell Hytte a AS | Real estate | 2019 |
| Kynningsrud AS | Construction | 1978 |
| Kynningsrud Capital AS | Construction | 2020 |
| Kynningsrud Eiendom AS | Real estate | 2008 |
| Kynningsrud Valle AS | Real estate | 2013 |
| Kr.Augustsgt. 1-3 A/S | Real estate | 1984 |
| Køhngården AS | Real estate | 2006 |
| L T S Holding AS | | 2026 |
| L-T Larsson Bygg & Skogkonsult | | 1999 |
| La-Vi AS | Real estate | 2012 |
| La-Vi Plastic Innovation AS | Professional & scientific | 2025 |
| Ladies Hundehus Da | Wholesale & retail | 1995 |
| Laft Invest AS | Administrative & support | 2024 |
| Lagre AS | Transport & logistics | 2010 |
| Lagre Minilager AS | Real estate | 2013 |
| Laky AS | Real estate | 2007 |
| Langvik Eiendom AS | Real estate | 2015 |
| Lannem Invest AS | Real estate | 2008 |
| Lare Eiendom AS | Real estate | 2015 |
| Larm Eiendom AS | Real estate | 2018 |
| Larm Skogsdrift AS | Agriculture & fishing | 2021 |
| Larnor AS | | 2022 |
| Lars Nikolai Invest AS | Wholesale & retail | 2005 |
| Larsen & Szefer Ans | Wholesale & retail | 1997 |
| Lasso AS | | 2023 |
| LBH AS | | 2024 |
| LDR AS | Transport & logistics | 2024 |
| Led Expert AS | Wholesale & retail | 1998 |
| Legene På Brygga AS | Health & social care | 2013 |
| Leid AS | Information & communication | 2016 |
| Leid Rental AS | Real estate | 2023 |
| Leie/Eie AS | Real estate | 2018 |
| Leif Grimsrud AS | Construction | 1982 |
| Leif Grimsrud Entreprenad AB | Construction | 2003 |
| Lekehuset Halden AS | Wholesale & retail | 2021 |
| Lemo Bygg AS | Real estate | 2000 |
| Lemo Invest AS | Real estate | 2005 |
| Lennart Larsson | Wholesale & retail | 2006 |
| Lennox Holding AS | | 2020 |
| Lerkegaarden Brukt Og Antikk AS | Wholesale & retail | 2022 |
| Levang AS | Wholesale & retail | 2007 |
| LF Bygg AS | Construction | 2023 |
| Liholt Hyttebygg Da | Construction | 2006 |
| Lilledal Holding AS | | 2021 |
| Lilletorget Halden AS | Real estate | 2005 |
| Lindhaugen Invest AS | Construction | 2005 |
| Lindquist AS | Construction | 2025 |
| Lineær Respons AS | Professional & scientific | 2025 |
| Linge Arkitektur AS | Professional & scientific | 2026 |
| Lintho Og Skogli Eiendom AS | Real estate | 2022 |
| Lirvall Holding AS | Transport & logistics | 2022 |
| Livsstilsklinikken Halden AS | Health & social care | 2022 |
| Ljlauritzen AS | Manufacturing | 2025 |
| Ljo AS | Real estate | 2021 |
| LK Kapital AS | | 2024 |
| LL Prosjekt AS | Real estate | 2011 |
| LMS Forvaltning AS | | 2023 |
| LN Clothing AS | Wholesale & retail | 2013 |
| Lofoten a Group AS | Wholesale & retail | 2022 |
| Loggator AS | Information & communication | 2013 |