| Rjukan Mur & Flis AS | Construction | 2015 |
| Rjukan Næringspark AS | Real estate | 2007 |
| Rjukan Næringsutvikling AS | Real estate | 1967 |
| Rjukan Synssenter AS | Wholesale & retail | 2018 |
| Rjukan Tannhelsesenter AS | Health & social care | 2001 |
| Rjukan Tannlegesenter AS | Health & social care | 2026 |
| Rjukan Technology Center AS | Real estate | 2010 |
| Rjukan Veterinærkontor AS | Professional & scientific | 2019 |
| Rjukan VVS & Elektro AS | Construction | 2000 |
| Robert Eidissen AS | | 2023 |
| Rve Holding AS | Real estate | 2024 |
| Sagaform AS | Wholesale & retail | 2017 |
| Sam Eydesgate 69 AS | Real estate | 2017 |
| Sam Eydesgt. 71 AS | Real estate | 2004 |
| Scolopendra AS | Real estate | 2017 |
| Skanem Rjukan AS | Manufacturing | 1996 |
| Skarpenord AS | Manufacturing | 1986 |
| Skiclub Partner AS | Real estate | 2018 |
| Skystjerne Holding AS | Information & communication | 2024 |
| Spak Consultants AS | Information & communication | 2015 |
| Spak Events AS | Administrative & support | 2024 |
| Spedify AS | Transport & logistics | 2021 |
| Sport 1 Gaustablikk AS | Wholesale & retail | 2015 |
| Sport 1 Rjukan AS | Wholesale & retail | 2021 |
| Stannum AS | Energy | 2020 |
| Stian Mårdalen AS | | 2019 |
| Storgata 19 AS | Real estate | 2002 |
| Storgata 20 AS | Real estate | 1979 |
| Styrvold Mat AS | Wholesale & retail | 2018 |
| Svadde Eiendom AS | Real estate | 2000 |
| Såheimsveien AS | Real estate | 2024 |
| Sønstaul Eiendom AS | Real estate | 2023 |
| Tannlege Gunnar Odd Hagen AS | Health & social care | 2004 |
| Team Klipp AS | Other services | 2005 |
| Telemark Kraft AS | Energy | 2020 |
| Telemark Maskin Og Import AS | Wholesale & retail | 2026 |
| Telemark Opplevelser AS | Administrative & support | 2001 |
| Telemark Stories AS | Information & communication | 2023 |
| Terrabon Norway AS | Energy | 2025 |
| Thomter Holding AS | Real estate | 2015 |
| Thomter Servicesenter AS | Other services | 2025 |
| Tinn Bilsenter AS | Other services | 2024 |
| Tinn Energi Eier AS | Energy | 2020 |
| Tinn Energi Og Fiber AS | Energy | 2000 |
| Tinn Energi Produksjon AS | Energy | 2001 |
| Tinn Engineering AS | Professional & scientific | 2005 |
| Tinn Tomteselskap AS | Real estate | 1985 |
| Tinn Utvikling AS | Real estate | 2011 |
| Tinndra AS | Hospitality | 2025 |
| Topborn AS | Information & communication | 2018 |
| Torben W Rasmussen AS | Administrative & support | 1997 |
| Torgeir Luraas AS | Administrative & support | 2022 |
| Tower Eiendom AS | Real estate | 1996 |
| Tinn Billag AS | Transport & logistics | 1936 |
| Tømrer Tommy Larsen AS | Construction | 2014 |
| Tømrer Torgeir Ingolfsland AS | Construction | 2012 |
| Veidemannens Jakt Og Fiske AS | Wholesale & retail | 2015 |
| Veset Gård Da | Agriculture & fishing | 2021 |
| Vetle Bjørtuft AS | Construction | 2013 |
| Vidda Explorer AS | Administrative & support | 2023 |
| Villsno AS | Wholesale & retail | 2024 |
| Visitrjukan AS | Administrative & support | 2003 |
| Vptt AS | Professional & scientific | 2022 |
| Vøle AS | Professional & scientific | 2023 |
| Westberg AS | Professional & scientific | 2019 |
| Wolfkat AS | Information & communication | 2022 |
| Word! Trine Dahlman AS | Arts & recreation | 2019 |
| Xtronica AS | Manufacturing | 2005 |
| Yngsett Eiendom AS | Real estate | 1978 |
| You&Me Rjukan AS | Wholesale & retail | 2014 |
| Ørnes AS | Real estate | 2005 |
| Ørnes Holding AS | Real estate | 1988 |
| Ørnes Sameie AS | Real estate | 2005 |
| Øverland Eiendom AS | Real estate | 1998 |
| Øystein Ørnes AS | Real estate | 2005 |