| Nygata 30 AS | Real estate | 2005 |
| Nygård Billedkunst AS | Arts & recreation | 2018 |
| Nyhaugen Invest AS | | 2021 |
| Nyhavn Holding AS | Financial services | 2015 |
| Nyhavna Eiendom AS | Real estate | 2021 |
| Nyhavna Infrastruktur AS | Construction | 2024 |
| Nyhavna Invest AS | | 2024 |
| Nyhavna Mekaniske AS | Real estate | 2006 |
| Nyhavna Studio Da | Information & communication | 2020 |
| Nyhavna Teknopark AS | Real estate | 2001 |
| Nyhavna Utvikling AS | Real estate | 2023 |
| Nyhavna Verkstedbygg AS | Real estate | 2023 |
| Nyheim Lodge AS | Hospitality | 2012 |
| Nylander & Partners AS | Real estate | 2006 |
| Nylander Invest AS | Real estate | 2020 |
| Nylander Næring AS | Real estate | 2006 |
| Nylandet Entreprenør AS | Construction | 2022 |
| Nylund AS | Real estate | 1993 |
| Nylund Invest AS | Real estate | 2007 |
| Nynotech AS | Information & communication | 2024 |
| Nypan AS | Professional & scientific | 2025 |
| Nyre & Breuer AS | Information & communication | 2024 |
| Nyrudveien 4 Eiendom AS | Real estate | 2014 |
| Nyskjerrigbarn AS | Wholesale & retail | 2026 |
| Nytt Hjem Eiendomsutvikling AS | Real estate | 2020 |
| Nytt Hjem Holding AS | Real estate | 2020 |
| Nytt Hjem Renovering AS | Real estate | 2021 |
| Nytteverdi AS | Professional & scientific | 2014 |
| Neufeldtsgt 3 AS | Households | 1950 |
| Nonnegaten 3 A/S. | Households | 1954 |
| Nær Engros Trondheim Cash & Carry AS | Wholesale & retail | 2015 |
| Nærbyen 24/7 AS | Real estate | 2017 |
| Nærbyen Boligsalg AS | Real estate | 2018 |
| Nærbyen Parkering AS | Real estate | 2018 |
| Nærbyen Utleiebolig AS | Real estate | 2018 |
| Næringsbygg AS | Construction | 2017 |
| Næss Dame & Herrefrisør Trondheim AS | Other services | 2020 |
| Nørd Holding AS | | 2022 |
| Nørstebø Invest AS | | 2021 |
| Nøst Holding AS | Financial services | 2018 |
| O & R Holding AS | Construction | 2007 |
| O Ofstad & Co AS | Real estate | 1968 |
| O Rydning Eiendom Ans | Real estate | 1996 |
| O'Persa AS | | 2021 |
| O. C. Bentzen AS | Real estate | 2005 |
| O. Hovde AS | | 1999 |
| O. L. Holding AS | Wholesale & retail | 1992 |
| O.R Rørservice AS | Construction | 2018 |
| O.Ø. Holding AS | | 2018 |
| O2 Sport Invest AS | | 2026 |
| O2 Sport Trondheim AS | Wholesale & retail | 2026 |
| O2 Sport Trondheim AS | Wholesale & retail | 2003 |
| Oak Capital AS | | 2024 |
| Oanor AS | Hospitality | 2025 |
| Oase AS | Real estate | 2018 |
| Oasen Kiosk AS | Wholesale & retail | 2024 |
| Oasis Movies Ans | Administrative & support | 2005 |
| Oaw Invest AS | | 2020 |
| Obatel AS | Real estate | 2014 |
| Obel Invest AS | Professional & scientific | 2017 |
| Obh Energi AS | Energy | 2026 |
| Obron Gruppen AS | Professional & scientific | 2012 |
| Obv 38 AS | Real estate | 2017 |
| Obv 41 AS | Financial services | 2020 |
| Occi Facility Management AS | Real estate | 2021 |
| Ocean Access AS | Information & communication | 2020 |
| Ocean Power Parks AS | Professional & scientific | 2021 |
| Ocean Space Acoustics AS | Information & communication | 2018 |
| Ocean Space Capital AS | Agriculture & fishing | 2019 |
| Oceantech Innovation AS | Professional & scientific | 2017 |
| Oceanx AS | Professional & scientific | 2018 |
| Ocelli AS | Information & communication | 2026 |
| Oco International Norge Nuf | Professional & scientific | 2010 |
| Octi AS | Professional & scientific | 1991 |
| Oda Ryggen Invest AS | | 2025 |
| Odd AI Holding AS | | 2020 |
| Odd Husbys Veg 52 AS | Real estate | 2023 |
| Odd Håkon Byberg Holding AS | Professional & scientific | 2018 |
| Odd Kapital AS | | 2025 |
| Odd Reitan Private Holding AS | Real estate | 2015 |
| Odd Roar Singstad AS | Administrative & support | 2005 |
| Odd Trandem Holding AS | | 2019 |
| Oddworks AS | Professional & scientific | 2011 |
| Odel & Eie AS | | 2017 |
| Odin Aero AS | Professional & scientific | 2006 |
| Oee Eiendom AS | Real estate | 2025 |
| Oee Holding AS | Real estate | 2005 |
| Oerens AS | Real estate | 2012 |
| Oets Holding AS | | 2025 |
| Ofa Forvaltning AS | Administrative & support | 2021 |
| Ofa Holding AS | | 2026 |
| Offscript Holding AS | | 2026 |
| Offshorelegen AS | Health & social care | 2023 |
| Offtrack AS | Wholesale & retail | 2009 |
| Ogf Boligutvikling AS | Real estate | 2026 |
| Ogf Holding AS | | 2023 |
| Ogj 691 Holding AS | | 2023 |
| Ohana Consulting AS | Arts & recreation | 2022 |
| Ohhm Holding AS | | 2025 |
| Ohlangen Holding AS | Real estate | 2020 |