| Donard Dental Laboratories Ltd | Manufacturing | 2013 |
| Donard Recruitment Ltd | Administrative & support | 2015 |
| Donard Rentals Ltd | Real estate | 2018 |
| Donard Wind Limited | Energy | 2016 |
| Donatellos Oldpark Limited | Other services | 2025 |
| Donedealni Limited | Extraterritorial | 2021 |
| Donegal Grill Ltd | Hospitality | 2024 |
| Donegall Enterprises Limited | Real estate | 2017 |
| Donegall Mews Management Company Limited | Extraterritorial | 2001 |
| Donegall Park Mews Management Co Limited | Households | 2013 |
| Donegall Pass CE | Health & social care | 2020 |
| Donegall Pass Community Forum | Other services | 2016 |
| Donegall Pass Property Management Limited | Households | 2004 |
| Donegall Place Invest Limited | Financial services | 2011 |
| Donegall Place Investments Limited | Real estate | 1994 |
| Donegall Properties Ltd | Real estate | 2023 |
| Donegall Quay Management Company Limited | Real estate | 2005 |
| Donegall Road Vintners Limited | Wholesale & retail | 2012 |
| Doneld Ltd | Information & communication | 2025 |
| Dong HOA AI Data Generation Ltd | Information & communication | 2025 |
| Dongchuanshun Limited | Wholesale & retail | 2024 |
| Dongming Lion Limited | Wholesale & retail | 2025 |
| Donkey Work Design Ltd | Professional & scientific | 2021 |
| Donlav Properties Limited | Real estate | 2019 |
| Donlea NI Limited | Households | 2024 |
| Donlin Investments Ltd | Real estate | 2019 |
| Donnelly Care Group Limited | Health & social care | 2017 |
| Donnelly Glackin Ltd | Hospitality | 2014 |
| Donnelly HR Limited | Administrative & support | 2015 |
| Donnybrook (Holdings) Limited | Professional & scientific | 2017 |
| Donnybrook (Plot 24) Limited | Financial services | 2024 |
| Donnybrook Court Management Company Limited | Extraterritorial | 2002 |
| Donnybrook Retail Limited | Professional & scientific | 2010 |
| Donquz Ltd | Wholesale & retail | 2025 |
| Donsenh Ltd | Wholesale & retail | 2025 |
| Donwall Limited | Real estate | 2000 |
| Dooish Wind Farm Holdings Limited | Financial services | 2022 |
| Dooish Wind Farm Limited | Energy | 2007 |
| Doon Limited | Other services | 2003 |
| Doone Plumbing and Heating Ltd | Construction | 2024 |
| Dooova Ltd | Information & communication | 2025 |
| Door Handles Limited | Extraterritorial | 2009 |
| Door Store Holdings Limited | Financial services | 2022 |
| DOOR-2-DOOR Cabs Ltd | Transport & logistics | 2018 |
| Doorstep Properties Ltd | Real estate | 2004 |
| Doorsteps (N.I.) Limited | Wholesale & retail | 2019 |
| Doran Consulting Corporation Limited | Professional & scientific | 2025 |
| Doran Consulting Group Limited | Professional & scientific | 2023 |
| Doran Consulting Limited | Professional & scientific | 2005 |
| Dorh Limited | Information & communication | 2024 |
| Dorigod Trading Limited | Wholesale & retail | 2025 |
| Dorman Holdings Limited | Financial services | 2020 |
| Dorn Limited | Real estate | 1996 |
| Dornan Property Maintenance Ltd | Construction | 2025 |
| Dornan Thermal Insulation Ltd | Construction | 2020 |
| Dornier Antretter Ltd | Wholesale & retail | 2024 |
| Dorsub (DPR) Limited | | 1992 |
| DOT Projects Design Ltd | Professional & scientific | 2020 |
| Dotsy Investments Limited | Professional & scientific | 2016 |
| Double Band Films Limited | Information & communication | 1987 |
| Double Bubble Smart Filter Ltd | Wholesale & retail | 2024 |
| Double Donut Limited | Wholesale & retail | 2025 |
| Double Glazing Supplies (Northern Ireland) Limited | | 1991 |
| Doublestar Overseas L.P. | | 2017 |
| Dougan Consulting Group Ltd | Professional & scientific | 2026 |
| Dougan Property Consultants Ltd | Real estate | 2014 |
| Douglas Bailie Golf Ltd | Wholesale & retail | 2013 |
| Douglas Fairweather Limited | Professional & scientific | 2023 |
| Douglas Huston Limited | Professional & scientific | 2006 |
| Douglas Huston LLP | | 2009 |
| Dougold Investments Limited | Financial services | 2025 |
| Dougold Partners Limited | Professional & scientific | 2022 |
| Dove Developments (NI) Limited | Construction | 2010 |
| Doverbrooke Limited | Wholesale & retail | 2025 |
| Dowds Transport Limited | Transport & logistics | 2012 |
| Dowling Financial Planning (DFP) Limited | Financial services | 2012 |
| Down County Homes Limited | Construction | 2021 |
| Down Marine Company Limited | Wholesale & retail | 1971 |
| Down NI Property Ltd | Construction | 2026 |
| Down Patriot Graves Limited | Other services | 2014 |
| Downe NIB Limited | Extraterritorial | 2021 |
| Downey Birch Ltd | Administrative & support | 2007 |
| Downey Osborne Ltd | Administrative & support | 2023 |
| Downferm Development Co. Ltd | Real estate | 2000 |
| Downhill Management Company Limited | Extraterritorial | 2005 |
| Downpadraig Distillery Co Ltd | Manufacturing | 2020 |
| Downpatrick Group Limited | Administrative & support | 2018 |
| Downpatrick Sports Centre Limited | Arts & recreation | 2014 |
| Downshire Developments Limited | Real estate | 1998 |
| Downshire Hall Management Company Limited | Households | 2018 |
| Downshire House Ltd | Extraterritorial | 2025 |
| Downshire Properties Ltd | Real estate | 2023 |
| Downshire Property Developers Ltd | Extraterritorial | 2000 |
| Downshire Sarre Ltd | Information & communication | 2006 |
| Downtown Radio Limited | Information & communication | 1974 |
| Downtown Tours Limited | Transport & logistics | 2025 |
| Downview Inns Ltd | Hospitality | 2012 |
| Downview Lodge Residents Limited | Households | 1987 |
| Downview Manor Management Company Limited | Extraterritorial | 2004 |
| Downview Park (Management) Limited | Professional & scientific | 1988 |