| Kslive AS | Professional & scientific | 2018 |
| KTS Bygg AS | Construction | 2014 |
| KTS Bygg Eiendom AS | Real estate | 2007 |
| KTS Holding AS | Real estate | 2020 |
| Kvamme Invest AS | Real estate | 1996 |
| Kåsastul Holding AS | | 2014 |
| Kåsastul Maskin AS | Construction | 2023 |
| Kåsin Vakt Og Sikkerhet AS | Administrative & support | 2026 |
| L-Tek AS | Professional & scientific | 2022 |
| Landsverk Eiendom AS | Real estate | 2011 |
| Landsverk Invest AS | Real estate | 2005 |
| Landvik Holding AS | Real estate | 2005 |
| Langedok Holding AS | | 2026 |
| Langkaasveien Utleie AS | Administrative & support | 2025 |
| Lauvåsvegen I Notodden SA | Real estate | 1940 |
| Leland Expeditions AS | Education | 2023 |
| Lepus Semantisk Web AS | Information & communication | 2024 |
| Liada AS | Real estate | 2020 |
| Lid Eiendom AS | Real estate | 1999 |
| Lidalen AS | Mining & quarrying | 2005 |
| Lidalen Grustak A/S | Mining & quarrying | 1977 |
| Lidvard Arvesen AS | Wholesale & retail | 1998 |
| Lien Varme Og Energi AS | Wholesale & retail | 1996 |
| Linna AS | Hospitality | 2025 |
| Linna Invest Og Utleie Ltd Nuf | Administrative & support | 2017 |
| Lisbeths Lille Gavehus AS | Wholesale & retail | 2023 |
| Lisleherad Montessoriskole SA | Education | 2013 |
| Lizzi Klær AS | Wholesale & retail | 2010 |
| Ljos Holding AS | Wholesale & retail | 2005 |
| Ljosland Invest AS | Real estate | 1988 |
| Ljosland Musikk AS | Wholesale & retail | 1997 |
| LJS AS | Wholesale & retail | 2021 |
| LK Autoinvest AS | Wholesale & retail | 2025 |
| Lmserv AS | Professional & scientific | 2017 |
| Lodestar Defence AS | Professional & scientific | 2026 |
| Lokal-Spillet AS | Professional & scientific | 2023 |
| LP Produksjon AS | Manufacturing | 2026 |
| Lure Kraft AS | Energy | 2021 |
| Lys Opp AS | Real estate | 2024 |
| Lystang AS | Hospitality | 2024 |
| Løvflaten Eiendom AS | Real estate | 2018 |
| M2N Holding AS | | 2026 |
| Madita AS | Hospitality | 2022 |
| Malermester Evensen AS | Construction | 1993 |
| Mamy Invest AS | Real estate | 2016 |
| Mannskapsutleie AS | Construction | 2015 |
| Marcus Aurelius AS | | 1993 |
| Mari Bakken AS | | 2020 |
| Martinsen Renhold & Vedlikeholdstjenester AS | Administrative & support | 2021 |
| Maskin & Service AS | Construction | 2019 |
| Mattverk AS | Professional & scientific | 2026 |
| Maxmin AS | Professional & scientific | 2017 |
| Mbe Notodden AS | Wholesale & retail | 2023 |
| MDN Transport AS | Transport & logistics | 2020 |
| Meetcon AS | Information & communication | 2006 |
| Meieribygget AS | Real estate | 1990 |
| Membranservice AS | Construction | 2015 |
| Merde Eiendom AS | Real estate | 2006 |
| Merdevegen 4B AS | Wholesale & retail | 2017 |
| Merdevegen 6 AS | | 2017 |
| Merdeveien 12 AS | Water & waste | 2012 |
| Merdeveien 14 AS | Real estate | 2021 |
| Merdeveien 2 AS | Real estate | 2020 |
| Merdeveien Eiendom AS | Real estate | 2012 |
| Mersmak I Notodden AS | Hospitality | 2020 |
| Mestringshusene Bolkesjø AS | Health & social care | 2016 |
| Midt Telemark Utleie AS | Administrative & support | 2020 |
| Midt-Telemark Hytteutvikling AS | Real estate | 2021 |
| Midtbøen Gård Da | Agriculture & fishing | 2021 |
| Mikkelborg AS | Wholesale & retail | 2013 |
| Minigravemaskiner AS | Construction | 1997 |
| Miniworker AS | Administrative & support | 2011 |
| Minox Technology AS | Professional & scientific | 1995 |
| Mitt Smil AS | Health & social care | 2017 |
| MJJ Eiendom AS | Real estate | 2013 |
| Mjva Holding AS | Wholesale & retail | 2022 |
| Mjva Import AS | Wholesale & retail | 2022 |
| Mobas AS | Construction | 2013 |
| Mobas Eiendom AS | Construction | 2016 |
| Mobas Industri AS | Real estate | 2017 |
| Mochas Collections Investment Limited | | 2025 |
| Mochas Collections Limited Nuf | Information & communication | 2025 |
| Modulcamp AS | Construction | 2024 |
| Moen-Consult AS | Professional & scientific | 2021 |
| Mogen Eiendom Miland AS | Construction | 2015 |
| Moland Holding AS | | 2025 |
| Moment Engineering AS | Professional & scientific | 2018 |
| Morgedal Drift Og Vedlikehald AS | Administrative & support | 2004 |
| Motstrøms AS | Wholesale & retail | 2016 |
| MRT Eiendom AS | Real estate | 2025 |
| MRT Holding AS | Wholesale & retail | 2023 |
| Murer Partner AS | Construction | 2023 |
| Murstad Entreprenørservice AS | Construction | 2016 |
| Muse AS | Professional & scientific | 2022 |
| My Pizza Notodden AS | Hospitality | 2021 |
| Myhorizon AS | Professional & scientific | 2025 |
| Mytech Holding AS | | 2025 |
| Naderia AS | Arts & recreation | 2022 |
| Natursport Da | Administrative & support | 2005 |
| ND Real Estate I AS | Real estate | 2021 |