| Northcroft Investments Limited | Financial services | 2003 |
| Norvic Consulting Ltd. | Information & communication | 2014 |
| Nostea Limited | Construction | 1976 |
| Nothe Fort Trading Company Limited | Wholesale & retail | 2015 |
| Nouveau Tattoo and Aesthetics Limited | Arts & recreation | 2024 |
| Nova Ripples Ltd | Financial services | 2026 |
| Novaco Design Ltd | Professional & scientific | 2022 |
| NPT Procurement Services Ltd | Professional & scientific | 2016 |
| NRH Dorset Limited | Wholesale & retail | 2016 |
| NS Jerk Kitchen Ltd | Wholesale & retail | 2025 |
| Nsab Limited | Real estate | 2026 |
| NU20 Management Company Ltd | Real estate | 2020 |
| Number 3 Management Company Limited | Administrative & support | 2004 |
| Nutmeg Studio Limited | Professional & scientific | 2013 |
| O P Plastering Limited | Construction | 2003 |
| O.S Landscapes Limited | Administrative & support | 2022 |
| Oakes Insurance Brokers Ltd | Financial services | 2017 |
| Oaktree Business Consultants Ltd | Administrative & support | 2023 |
| Oaktree Stores Limited | Wholesale & retail | 2010 |
| Oasis Property & Rentals Limited | Real estate | 2025 |
| OBM Architectural Management Limited | Construction | 2007 |
| OCA Solutions Limited | Manufacturing | 2013 |
| Ocean Court (Weymouth) Management Company Ltd | Other services | 2003 |
| Ocean Electric Limited | Manufacturing | 2009 |
| Ocean Estates Limited | Hospitality | 2000 |
| Ocean Pizza Weymouth Ltd | Hospitality | 2018 |
| Ocean Therapy Limited | Health & social care | 2015 |
| Ocean Wave Technology Ltd | Information & communication | 2001 |
| Oceans 99 Limited | Hospitality | 2017 |
| Oceanside Investments Limited | Real estate | 2022 |
| Oddjob-A-Bility Maintenance Ltd | Administrative & support | 2011 |
| Oddo Games Ltd | Information & communication | 2024 |
| OEB Limited | Financial services | 2026 |
| Oemb Limited | Financial services | 2026 |
| Officers Field Management Company Limited | Households | 2011 |
| OKE AD Retail Ltd | Wholesale & retail | 2025 |
| Okeford Farm Limited | Agriculture & fishing | 2025 |
| OLA Skyline Retail Ltd | Wholesale & retail | 2025 |
| Old Bridge Court (Management) Limited | Households | 1988 |
| Old Castle Hotel Limited | Hospitality | 2018 |
| Old Coastguards Management Co. Ltd. | Real estate | 2011 |
| Old Harbour Dive Centre Limited | Arts & recreation | 2017 |
| Oliver Harris Ltd | Information & communication | 2017 |
| Oliveto Limited | Hospitality | 2021 |
| Olsen Estates Ltd | Real estate | 2020 |
| OM Holidays Ltd | Agriculture & fishing | 1958 |
| OMA Property (Dorset) Ltd | Real estate | 2022 |
| Omers Traditional Turkish Barbers Ltd | Other services | 2023 |
| Omnilodge Limited | Households | 1987 |
| ON Property Limited | Real estate | 2012 |
| ON the Mark Building and Electrical Services Ltd | Construction | 2023 |
| ON WAX Ltd | Hospitality | 2026 |
| ON Your Case Limited | Transport & logistics | 2008 |
| ON Your Case Property Limited | Manufacturing | 2019 |
| One Barrel Properties Ltd | Real estate | 2018 |
| One Eleven Projects Limited | Construction | 2021 |
| One TEN Kite & Wing Ltd | Education | 2024 |
| Only Just Ltd | Wholesale & retail | 2011 |
| Operis Consulting Ltd | Information & communication | 2015 |
| Operis Developments Limited | Real estate | 2011 |
| Opportunities R UN Limited | Education | 2014 |
| OPS Management Limited | Administrative & support | 2015 |
| Optimum Agility Limited | Information & communication | 2020 |
| Optionground Property Management Limited | Households | 1991 |
| Opus Royalties Limited | Professional & scientific | 2017 |
| Oracle Estates Limited | Real estate | 2004 |
| Orchard Health Consultancy Limited | Other services | 2008 |
| Orchard Properties (Dorset) Limited | Real estate | 2015 |
| Organising Limited | Administrative & support | 2014 |
| Original Chalk Limited | Education | 2015 |
| Osmington Holiday Park Limited | Financial services | 2019 |
| Osmington Homes Limited | Construction | 2000 |
| Osprey Road Management Company Limited | Households | 2017 |
| Ostinato Rigore Solutions Ltd | Professional & scientific | 2024 |
| Otter Cottage Ltd | Real estate | 2025 |
| Ottoman Kebab House Weymouth Ltd | Hospitality | 2021 |
| OUR Secret Aesthetics Ltd | Other services | 2020 |
| Outdoor Education Services Group Ltd | Education | 2018 |
| Overcombe Financial Solutions Ltd | Financial services | 2024 |
| Overcombe House Management Limited | Extraterritorial | 1995 |
| Overwatch Tactical Solutions Limited | Professional & scientific | 2025 |
| Oxford Maintenance Services Ltd | Construction | 2021 |
| Oxleycare Ltd | Other services | 2000 |
| Ozzie Enterprises LLP | | 2009 |
| P & a Moore Ltd | Financial services | 2015 |
| P & D Contracts Weymouth Limited | Transport & logistics | 2002 |
| P & H Property Ltd | Real estate | 2026 |
| P Factor Ltd | Wholesale & retail | 2017 |
| P J Watts Independent Financial Adviser Ltd | Financial services | 2019 |
| P M Bastable Consultancy Services Limited | Professional & scientific | 2026 |
| P N Gray Electrical Limited | Manufacturing | 2014 |
| P&J Sons Properties Ltd | Real estate | 2026 |
| P&M Cleaning Services Ltd | Administrative & support | 2017 |
| P.C. Farriers Limited | Administrative & support | 2002 |
| P.E. Training Services Limited | Professional & scientific | 2016 |
| P.R. Howell Limited | Wholesale & retail | 2002 |
| P.S.W. Ltd. | Administrative & support | 1991 |
| Paint Works London Limited | Construction | 2007 |
| Paisley Plant Hire Limited | Construction | 2005 |
| Palittadnb Ltd | Professional & scientific | 2024 |