| JS Soccer Skills Limited | Arts & recreation | 2024 |
| JS Tradind Ltd | Wholesale & retail | 2026 |
| JSR Jointing Ltd | Construction | 2023 |
| JT Maxwell Limited | Information & communication | 2015 |
| JT Sheds & Joinery Lisburn Ltd | Construction | 2023 |
| Judabi Ltd | Professional & scientific | 2018 |
| Juvenile M Ltd | Health & social care | 2019 |
| JWG Engineering Solutions Limited | Professional & scientific | 2021 |
| JWK Haulage Ltd | Transport & logistics | 2022 |
| K & P Construction Ltd | Construction | 2021 |
| K D Hair Ltd | Other services | 2015 |
| K Toal Ltd | Health & social care | 2019 |
| K-Tec Machinery Ltd | Professional & scientific | 2023 |
| K9 Rehab Dog Training Ltd | Other services | 2025 |
| Kage Engineering (NI) Limited | Manufacturing | 2012 |
| Kaizen Care Limited | Health & social care | 2020 |
| Kansas Properties Ltd | Real estate | 2021 |
| Karat Trading LP | | 2018 |
| Karma Kalakendram | Arts & recreation | 2015 |
| Karmodo Ltd | Wholesale & retail | 2024 |
| KAS (N.I.) Ltd | Other services | 2014 |
| Kawz Limited | Health & social care | 2022 |
| KB Parcels Limited | Other services | 2024 |
| KB Sports Hub Ltd | Wholesale & retail | 2023 |
| KDB Property Limited | Households | 2022 |
| Kearney Consult Ltd | Construction | 2015 |
| Kearney Consulting Limited | Professional & scientific | 2024 |
| Kearney's Paper and Paint (2001) Limited | Wholesale & retail | 2001 |
| Keedis Ltd | Manufacturing | 2024 |
| Keel Holdings (N.I.) Limited | Real estate | 2024 |
| Keith Young Ltd | Wholesale & retail | 2025 |
| Kelly European Freight Services Limited | Transport & logistics | 2000 |
| Kelly Lighting (N.I.) Limited | Wholesale & retail | 2011 |
| Kelly Property Rentals Ltd | Real estate | 2024 |
| Kelly Transport Ltd | Transport & logistics | 2020 |
| Kelman Tavrida Group Limited | Manufacturing | 1997 |
| Kelso Agencies Limited | Wholesale & retail | 1979 |
| Kelso Kristen Bathrooms Limited | Wholesale & retail | 2003 |
| Kelvatek Monitoring Limited | Professional & scientific | 2005 |
| Kendal Developments Limited | Professional & scientific | 1996 |
| Kepes Ltd | Wholesale & retail | 2019 |
| Kerichem Materials Science Ltd | Wholesale & retail | 2025 |
| Kerr Fuels Ltd | Wholesale & retail | 2024 |
| Kerry Elizabeth Laser & Skin Clinic Ltd | Other services | 2024 |
| Keyes Castro DEL Cabo Limited | Information & communication | 2020 |
| Keystones Management LP | | 2024 |
| KFW Group Ltd | Wholesale & retail | 2003 |
| KGA Accountants LLP | | 2023 |
| KH Balmoral Estates Limited | Real estate | 2017 |
| KHAR1 Limited | Real estate | 2025 |
| KHD Investments Limited | Hospitality | 2015 |
| Kids Health Tech Ltd | Manufacturing | 2025 |
| Kidz Academy Ltd | Education | 2024 |
| Kieran Gilmurray and Company Limited | Information & communication | 2024 |
| Kildartan Investments Limited | Construction | 2008 |
| Kilkeel River Properties Limited | Real estate | 2016 |
| Killead Investments Limited | Financial services | 2021 |
| Killeenan Limited | Real estate | 2020 |
| Killsmullan Limited | Transport & logistics | 2012 |
| Killylane Properties Limited | Real estate | 2012 |
| Kilpatrick Associates Limited | Administrative & support | 2012 |
| Kilwinning Limited | Other services | 2009 |
| Kindergarden Cooks C.I.C. | Education | 2018 |
| King's Hall Exhibition & Conference Centre Limited - the | Arts & recreation | 1997 |
| King's Hall Harberton Estates Limited | Real estate | 2014 |
| Kingsberry Garden Management Ltd | Administrative & support | 2026 |
| Kingscourt Health Ltd | Health & social care | 2022 |
| Kingslodge Guest House Limited | Hospitality | 2012 |
| Kinva Health Ltd | Information & communication | 2022 |
| Kitted Cars NI Ltd | Wholesale & retail | 2020 |
| Kmca Limited | Other services | 2026 |
| KME Steelworks Ltd | Manufacturing | 1999 |
| Knight Service Affichage Obligatoire LP | | 2023 |
| Knightsbridgecarsni Limited | Wholesale & retail | 2016 |
| Knockany Limited | Real estate | 2020 |
| Knockmore Limited | Manufacturing | 2020 |
| Knockmore Road Hand Car Wash Ltd | Administrative & support | 2020 |
| Know Taxes Limited | Professional & scientific | 2025 |
| Knowles Flooring Ltd | Construction | 2018 |
| Knox & Clayton LLP | | 2013 |
| Knox Clayton Consarc Limited | Professional & scientific | 2022 |
| Koda's Coffee Bar Ltd | Hospitality | 2025 |
| Kotg Limited | Information & communication | 2013 |
| KP Digital Limited | Professional & scientific | 2020 |
| Kpcm Display Ltd | Administrative & support | 2015 |
| KPH Consultancy Ltd | Professional & scientific | 2021 |
| KPM Surfacing Ltd | Construction | 2012 |
| KQL Engineering Ltd | Professional & scientific | 2026 |
| Kremer Consultancy Services Ltd | Professional & scientific | 2003 |
| KTM Curry Limited | Hospitality | 2021 |
| Kulawe Consultancy Limited | Information & communication | 2018 |
| KVS Group (UK) Limited | Real estate | 2003 |
| KVS Properties Limited | Real estate | 2003 |
| L C Joiner and Build Limited | Construction | 2020 |
| L D Kitchens Ltd | Construction | 2017 |
| L Digger Services Ltd | Construction | 2018 |
| L Fast Foods Ltd | Hospitality | 2019 |
| L.C. Homes Management Limited | Households | 2002 |
| L.G. Portable Cabins Ltd | Construction | 2025 |
| L.G. Contracting Ltd | Construction | 1991 |