| Nu-Horizon Training Ltd | Professional & scientific | 1993 |
| OAG Renewables Limited | Energy | 2011 |
| Oiga Properties Ltd | Real estate | 2026 |
| Olgrinmore Forest Ltd | Agriculture & fishing | 2011 |
| ON the News Ltd | Information & communication | 2022 |
| Orbell Property Management Ltd | Construction | 2018 |
| Ormlie Community Association Ltd. | Health & social care | 2001 |
| P Ronai Painter & Decorator Ltd | Construction | 2019 |
| Parallel 58 Ltd | Information & communication | 2015 |
| Pasha Barbershop Ltd | Other services | 2025 |
| Pdqm Limited | Professional & scientific | 2004 |
| Penglas Planning Services Ltd | Professional & scientific | 2011 |
| Pennyland House Ltd | Hospitality | 2008 |
| Pentland Hotel | | 1997 |
| Petrie Painters Limited | Construction | 2013 |
| Phd/Barga Ltd | Hospitality | 2011 |
| Phoenix Fishing Company Ltd | Agriculture & fishing | 2020 |
| Phone Care Ltd | Wholesale & retail | 2023 |
| Pixelit (Scotland) Ltd | Information & communication | 2019 |
| PJ Sons Ltd | Other services | 2017 |
| Pollard Property and Mortgages Ltd | Financial services | 2021 |
| Pollards Estate and Letting Limited | Real estate | 2015 |
| Port Ghrant Ltd | Construction | 2016 |
| Precision Blinds Limited | Construction | 2003 |
| Precision Plumbing & Heating Thurso Ltd | Construction | 2020 |
| Puffin Cove Limited | Manufacturing | 2020 |
| R Gray Services Ltd | Construction | 2016 |
| R&K Robertson Properties Limited | Real estate | 2025 |
| R.R. Mackay & Company Limited | Agriculture & fishing | 1960 |
| RAD Protect Limited | Professional & scientific | 2023 |
| Ramsay Electrical Services Ltd | Construction | 2024 |
| RC Property Lets Ltd | Real estate | 2024 |
| RDI Renewables Limited | Construction | 2012 |
| Reay Holdings Limited | Wholesale & retail | 2021 |
| Reay Young-Stars CIC | Information & communication | 2023 |
| Reid & Fraser Audit Limited | Professional & scientific | 2021 |
| Reid & Fraser EOT Trustees Limited | Financial services | 2021 |
| Reid's Bakery (Thurso) Limited | Manufacturing | 2005 |
| Revive Therapies Ltd | Health & social care | 2024 |
| Rfishing Ltd | Agriculture & fishing | 2020 |
| RMM Scaff Ltd | Construction | 2023 |
| Ronai Industrial Paint Solutions Ltd | Manufacturing | 2019 |
| Rosegill Ltd | Agriculture & fishing | 2013 |
| Rova Housing Ltd | Real estate | 2025 |
| RP Alba Ltd | Professional & scientific | 2011 |
| S & a Forbes Services Ltd | Real estate | 2024 |
| S Blackwood Fabrication & Construction Services Ltd | Manufacturing | 2024 |
| S. Engineering Services Ltd. | Other services | 2015 |
| SB Access Ltd | Construction | 2015 |
| SCG Planning Limited | Professional & scientific | 2018 |
| Scrabster Engineering Services Limited | Manufacturing | 2013 |
| Scrabster Offshore Services Ltd | Extraterritorial | 2011 |
| Scrabster Seafoods Limited | Wholesale & retail | 1996 |
| Shiro Holidays Ltd | Hospitality | 2024 |
| Simpson & OAG Ltd | Construction | 2012 |
| SJM Agri Ltd | Professional & scientific | 2015 |
| Skerray Limited | Administrative & support | 2020 |
| Sky View Rentals Limited | Administrative & support | 2025 |
| Sordale Estates Limited | Real estate | 2025 |
| Spellbound Caithness Ltd | Wholesale & retail | 2022 |
| Spice House Thurso Ltd | Hospitality | 2024 |
| Splitstone Services Ltd | Wholesale & retail | 2021 |
| Stanley Nuclear Services Limited | Professional & scientific | 2024 |
| Stephen Okane Ltd | Construction | 2018 |
| Stillhouse Media Ltd | Wholesale & retail | 2025 |
| Stky Services Ltd | Professional & scientific | 2024 |
| Strathdon Scaffolding Ltd | Construction | 2026 |
| Straumsey Associates Ltd | Professional & scientific | 2020 |
| Straumsey Properties Limited | Real estate | 2017 |
| Subsea Construction Surveys Ltd | Professional & scientific | 2016 |
| Sudrland Services Ltd | Extraterritorial | 2024 |
| Superclean of Thurso Ltd | Administrative & support | 2017 |
| Sustainability Services Scotland Ltd | Professional & scientific | 2016 |
| Sutherland E C & I Ltd | Construction | 2023 |
| T Hush Ltd | Agriculture & fishing | 2025 |
| T8 Construction & Sons Ltd | Construction | 2023 |
| TAJ Mahal Indian Takeaway Limited | Hospitality | 2025 |
| Tall Tales Coffee Limited | Hospitality | 2026 |
| Tasty Cajun Shop Limited | Wholesale & retail | 2026 |
| TC Newco 20153 Limited | Extraterritorial | 2015 |
| THE Allt Beag Armadale Trust | Agriculture & fishing | 2001 |
| THE Gardeners Lounge Ltd | Other services | 2024 |
| THE Highland Alchemist Ltd | Extraterritorial | 2024 |
| THE Highland Haven Limited | Hospitality | 2017 |
| THE Home of Magick Limited | Wholesale & retail | 2025 |
| THE Northern Vault Ltd | Administrative & support | 2021 |
| THE Store Cafe Ltd | Hospitality | 2019 |
| THE Thurso & Caithness Hotel 2025 Ltd | Hospitality | 2025 |
| THE Thurso Bistro Ltd | Hospitality | 2026 |
| The-Mart Ltd | Information & communication | 2019 |
| Thomson International (Fish Sales) Limited | Wholesale & retail | 1999 |
| Thor Accountancy Ltd | Professional & scientific | 2018 |
| Thor Rentals Ltd | Hospitality | 2023 |
| Throttle Therapy Garage Ltd | Wholesale & retail | 2024 |
| Thurso Accommodation Ltd | Real estate | 2026 |
| Thurso Best Kebab (Caithness) Ltd | Hospitality | 2018 |
| Thurso Community Cafe CIC | Hospitality | 2019 |
| Thurso DIY Ltd | Wholesale & retail | 2023 |
| Thurso DIY Wholesale Ltd | Wholesale & retail | 2024 |
| Thurso Electrical Control Systems Limited | Manufacturing | 1997 |