| Noisy & Co Agency Ltd | Professional & scientific | 2025 |
| Nonna Peppina Bakery Ltd | Manufacturing | 2022 |
| Nonna Peppina Limited | Hospitality | 2020 |
| Nonno Peppe Ltd | Hospitality | 2020 |
| Norfolk Court (Bridport 2010) Management Company Limited | Households | 2010 |
| Norman's Business Consultancy Limited | Professional & scientific | 2025 |
| Norsand Limited | Real estate | 1988 |
| North Dorset Business Park Management Company Limited | Households | 2016 |
| Northern Energy Innovations Ltd | Wholesale & retail | 2023 |
| Northover Accountants LLP | | 2020 |
| Norwood Digital Ltd | Information & communication | 2025 |
| Nostrano DEL Brenta UK Limited | Wholesale & retail | 2017 |
| NOT Asleep NOT Awake Limited | Professional & scientific | 2024 |
| Nottington Court Management Limited | Households | 1973 |
| Notton Equine Assisted Learning C.I.C. | Education | 2021 |
| Nourivo Ltd | Wholesale & retail | 2025 |
| Novum Construction Limited | Extraterritorial | 2013 |
| Noyce Property Investments Ltd | Real estate | 2026 |
| Nsugg Limited | Professional & scientific | 2012 |
| Nugen Facilities Ltd | Administrative & support | 2018 |
| Nutley Farm Events Ltd | Administrative & support | 2009 |
| Nutri Cuisine Limited | Hospitality | 2004 |
| Nutri Essentials Ltd | Wholesale & retail | 2026 |
| NW Car Sales Limited | Wholesale & retail | 2012 |
| O K Lewis Ltd | Professional & scientific | 2025 |
| O T Event Technicians Ltd | Professional & scientific | 2023 |
| O'Pasta Ltd | Manufacturing | 2025 |
| O.H.E. Horticultural Limited | Wholesale & retail | 2001 |
| O.J. Fabrications Limited | Manufacturing | 2009 |
| OA Landscapes Limited | Administrative & support | 2025 |
| Oak Dorset Ltd | Construction | 2024 |
| Oakenstead Estates Limited | Construction | 1983 |
| Oaklands Avenue Chard Limited | Real estate | 2019 |
| Oakwell & INK Ltd | Wholesale & retail | 2026 |
| Oasis Wine Shop Limited | Wholesale & retail | 2013 |
| Obrien Roofing Ltd | Construction | 2018 |
| Obrien Scaffolding Ltd | Construction | 2015 |
| Obriens Building Ltd | Construction | 2024 |
| Obriens Group Ltd | Financial services | 2017 |
| Obriens Holdings Ltd | Real estate | 2016 |
| OC Renovations Ltd | Construction | 2018 |
| Ocean Trax Limited | Transport & logistics | 2021 |
| Ocean Ventures Limited | Professional & scientific | 2003 |
| Oceanbound Sailing Limited | Transport & logistics | 2022 |
| Oceans Detailing (Sandbanks) Limited | Wholesale & retail | 2020 |
| Octocorp Ltd | Administrative & support | 2013 |
| Octopus Initiative Limited | Manufacturing | 1999 |
| Octopus Property and Building Service Ltd | Construction | 2023 |
| Odcombe Garden Limited | Agriculture & fishing | 2026 |
| Offshore Rebel (Weymouth) Limited | Transport & logistics | 2017 |
| Oggetto Limited | Other services | 2011 |
| Ogon Ltd | Real estate | 2019 |
| Ohfmc Limited | Real estate | 2016 |
| OIL Heating Services Limited | Construction | 2010 |
| OJH Space Ltd | Construction | 2023 |
| Okeford Heating Limited | Construction | 2003 |
| Olariz Ltd | Professional & scientific | 2016 |
| Old Inn Mullion Ltd | Hospitality | 2024 |
| Old Mill (Misterton) Management Co Limited | Real estate | 2012 |
| Old Rectory Dorchester Management Company Limited | Households | 1991 |
| Olds Motor Group | Wholesale & retail | 1987 |
| Olds Welding Ltd | Administrative & support | 2002 |
| OLE Tennessee Limited | Hospitality | 2024 |
| Olivae Consulting Ltd | Professional & scientific | 2026 |
| Olivine Clinic Ltd | Health & social care | 2024 |
| Olympios Holdings Ltd | Real estate | 2019 |
| Omega Ventures Limited | Arts & recreation | 2014 |
| Omegadent Limited | Health & social care | 2022 |
| ON Track Safaris Ltd | Administrative & support | 2015 |
| Oncharge EV Ltd | Construction | 2025 |
| One & Done Group Ltd | Administrative & support | 2026 |
| One Body Health Ltd | Health & social care | 2026 |
| One Harbour View RTM Co. Limited | Households | 2010 |
| Oneworld Aviation Management Limited | Professional & scientific | 2001 |
| Online Textiles Ltd | Wholesale & retail | 2021 |
| Online Vitamins Limited | Wholesale & retail | 2012 |
| Only Pet Food Ltd | Wholesale & retail | 2021 |
| Onurmert Limited | Wholesale & retail | 2012 |
| Oovavoo Ltd | Information & communication | 2013 |
| Open Air Dairy Limited | Agriculture & fishing | 2017 |
| Optimysport Ltd | Education | 2024 |
| Orange Oak Enterprises Ltd. | Administrative & support | 2011 |
| Orbit DJ Retreats Limited | Education | 2019 |
| Orcatech Limited | Information & communication | 2025 |
| Orchard Vale Property Developments Limited | Construction | 2001 |
| Orchid Farm (Plush) Limited | Households | 1994 |
| Original ASH Ltd | Professional & scientific | 2026 |
| Oriole Travel Ltd | Transport & logistics | 2024 |
| Orlando James Limited | Professional & scientific | 2014 |
| Orpa (Wessex) Limited | Other services | 2020 |
| OST Eatery Ltd | Hospitality | 2023 |
| Ostium Homes Limited | Construction | 2020 |
| Ottons Limited | Administrative & support | 2020 |
| Overcombe Court Limited | Households | 1978 |
| Owen Matthews Associates Limited | Financial services | 2002 |
| OWL Scientific Limited | Professional & scientific | 2022 |
| Oxbridge Founders Limited | Information & communication | 2024 |
| Ozmo Motorsport Performance Centre Ltd | Wholesale & retail | 2021 |
| P & J Dennison Ltd | Agriculture & fishing | 2017 |
| P & M Event Caterers Limited | Hospitality | 2021 |