| J. Cheesmur & Sons (Lewes) Limited | Construction | 1998 |
| J. Sloane Limited | Professional & scientific | 2011 |
| J.& H.Robinson(Iford Farms)Limited | Agriculture & fishing | 1941 |
| J.E. Evans (Insurance) Limited | Real estate | 1963 |
| J.F.L. Properties Limited | Real estate | 1963 |
| J.J. Hatfield & Company Limited | Professional & scientific | 1987 |
| Jack Bartholomew Racing Ltd | Arts & recreation | 2021 |
| Jacksonbreen Limited | Information & communication | 2020 |
| Jaks Party Power Limited | Construction | 2018 |
| JAL Logistics Ltd | Transport & logistics | 2025 |
| James Breckell Architects Limited | Professional & scientific | 2003 |
| James Dale Associates Limited | Administrative & support | 2006 |
| James FOX Consulting Ltd | Professional & scientific | 2013 |
| James Price Blacksmith Limited | Manufacturing | 2011 |
| James Snell Electrical Limited | Construction | 2014 |
| Jamieson Support Ltd | Health & social care | 2022 |
| Jandaque Property Services Limited | Households | 2022 |
| Jasmin Vardimon Company Limited | Education | 2001 |
| Jasmine Analytics Ltd | Professional & scientific | 2010 |
| Jayden Consultants Limited | Professional & scientific | 1998 |
| Jays Autos Sussex Ltd | Wholesale & retail | 2020 |
| Jazzlaw Ltd | Professional & scientific | 2011 |
| JB Controls Limited | Professional & scientific | 2020 |
| Jcep Sussex Limited | Other services | 2025 |
| JCK Martial Arts Ltd | Arts & recreation | 2024 |
| JDF Energy Limited | Professional & scientific | 2020 |
| JDG Specialist Consultancy Services Ltd | Professional & scientific | 2021 |
| JGC Kitchens KH Ltd | Hospitality | 2026 |
| Jimfest Ltd | Arts & recreation | 2023 |
| JIT13 Limited | Other services | 2024 |
| JJ Ideas Limited | Manufacturing | 2004 |
| JMC Program Management Ltd | Professional & scientific | 2026 |
| JMD Building & DIY Supplies Ltd | Wholesale & retail | 2018 |
| JNP Docendo Ltd | Administrative & support | 2013 |
| Joana Dias Locum Services Ltd | Professional & scientific | 2025 |
| Joanna & Adam LLC | | 2023 |
| Jobeeny Limited | Manufacturing | 2007 |
| Jodyenterprises Ltd | Wholesale & retail | 2018 |
| JOE Orton Ltd | Information & communication | 2021 |
| Joem Consulting Limited | Professional & scientific | 2019 |
| John Avon Art Limited | Arts & recreation | 2014 |
| John Christie,Limited | Financial services | 1934 |
| John Gage Limited | Hospitality | 1985 |
| John Gosnell & Company,Limited | Manufacturing | 1933 |
| John Monnington Farms Limited | Agriculture & fishing | 1957 |
| John S. Pile (Farms) Limited | Agriculture & fishing | 1966 |
| Joka Holdings Ltd | Manufacturing | 2023 |
| Jolu Development Consultants Ltd | Other services | 2020 |
| Jolu Holdings Ltd | Real estate | 2021 |
| JON Barnes Ltd | Professional & scientific | 2021 |
| Jonily Ltd | Real estate | 2023 |
| Jonny KAY Consultancy Limited | Education | 2026 |
| Joshua Charles Developments Limited | Real estate | 2002 |
| Josie Smart Interiors Ltd | Professional & scientific | 2025 |
| Joughin Medical Limited | Health & social care | 2024 |
| Joy Delight Ltd | Hospitality | 2026 |
| Jstax & Co Ltd | Wholesale & retail | 2025 |
| Jtbaldwin Electrical Ltd | Construction | 2025 |
| Juggs Close (Management Company) Limited | Households | 1995 |
| Junor & Davies Limited | Administrative & support | 2024 |
| Jupitus Ltd | Professional & scientific | 2004 |
| Just Cool IT Limited | Administrative & support | 2009 |
| Just Dough IT Ltd | Hospitality | 2024 |
| Just Pure Software Ltd | Information & communication | 2013 |
| JY Red Envelope Limited | Hospitality | 2025 |
| K H Lewes Limited | Hospitality | 2019 |
| K Jenner Carpenter Ltd | Administrative & support | 2017 |
| K-Seal International Limited | Wholesale & retail | 2015 |
| Kadt Limited | Professional & scientific | 2023 |
| Kaege Limited | Financial services | 2018 |
| Kalogerides Consulting Ltd | Information & communication | 2013 |
| Kanssa International Ltd | Wholesale & retail | 2023 |
| Karen Branagh Consultancy Limited | Administrative & support | 2023 |
| Kate Wood Communications Ltd | Administrative & support | 2017 |
| Katie Fitzsimons Ltd | Manufacturing | 2018 |
| KC Healthier Organisations Ltd | Professional & scientific | 2021 |
| KCC Consulting Limited | Professional & scientific | 2025 |
| KDW NDT & Inspection Services Ltd | Professional & scientific | 2026 |
| Keen Industries Ltd | Information & communication | 2020 |
| Keeys Autos Ltd | Wholesale & retail | 2021 |
| Keeys Mots Ltd | Professional & scientific | 2025 |
| KEG Catering Consultants Limited | Hospitality | 2007 |
| Keizer Frames Limited | Manufacturing | 2014 |
| Kelb Nominees Limited | Professional & scientific | 2019 |
| Kelvin Bromley Consulting Limited | Professional & scientific | 2023 |
| Kelvin Business Centre Limited | Real estate | 2024 |
| Kemp Town Catering Company Limited | Hospitality | 2019 |
| Ketches Holdings Limited | Financial services | 2024 |
| Key Risk Consulting Limited | Information & communication | 2015 |
| Keystone Commercial Ltd | Professional & scientific | 2025 |
| KH London Trading Ltd | Manufacturing | 2025 |
| Kihlstrom and Associates Advisory Services Limited | Professional & scientific | 2009 |
| Killzone Pest Control Ltd | Administrative & support | 2026 |
| Kilnwood Management Company Limited | Real estate | 2018 |
| KIM Kong Kimchi Limited | Manufacturing | 2017 |
| KIM Sheard Design Ltd | Professional & scientific | 2023 |
| Kind Sustainable Supplies Ltd | Wholesale & retail | 2021 |
| Kings Church Centre, Lewes | Other services | 2000 |
| Kingston Independent Financial Services Ltd | Financial services | 2021 |
| Kinloch Rannoch Residential Ltd | Real estate | 2024 |