| James Smith (Accountant) Limited | Professional & scientific | 2003 |
| Janc Consulting Limited | Administrative & support | 2020 |
| Janc Holdings Limited | Real estate | 2017 |
| Jauntree Limited | Households | 1982 |
| JCB Heating Limited | Construction | 2019 |
| JCF Consultancy Ltd | Professional & scientific | 2024 |
| JCH Hanney Ltd | Construction | 2019 |
| Jenssen Architecture Limited | Professional & scientific | 2012 |
| Jeremy Wagg Limited | Manufacturing | 2021 |
| Jeskei Limited | Information & communication | 2020 |
| Jess Simpson Limited | Professional & scientific | 2017 |
| Jesse Composite Limited | Professional & scientific | 2016 |
| JKJ Design Ltd | Professional & scientific | 2022 |
| JM Animal Therapy Ltd | Professional & scientific | 2025 |
| Joanna Rees Limited | Administrative & support | 1999 |
| Joanna Ruth Bell Foundation | Health & social care | 2023 |
| John Lewis of Hungerford Limited | Manufacturing | 1977 |
| JON Atkins & Associates Ltd | Professional & scientific | 2018 |
| Jordachemoore Limited | Construction | 2018 |
| Joshmerrett Limited | Other services | 2023 |
| Joshua Thomas Finance Ltd | Financial services | 2019 |
| Joshua Thomas Homes Ltd | Real estate | 2022 |
| Josiane Light Ltd | Wholesale & retail | 2024 |
| Josy Properties Limited | Real estate | 2022 |
| JP Terry Carpentry & Building Services Ltd | Construction | 2018 |
| Jp&P Consulting Limited | Professional & scientific | 2010 |
| Jp&P Group Limited | Financial services | 2020 |
| Jpaq Limited | Wholesale & retail | 2021 |
| JR Nuclear Limited | Professional & scientific | 2013 |
| JSD Projects Limited | Health & social care | 2022 |
| JT Stage Productions Ltd | Arts & recreation | 2018 |
| Judith Humberstone Ltd | Professional & scientific | 2008 |
| Juja Services Ltd | Hospitality | 2025 |
| Julia Long Consultants Limited | Health & social care | 2009 |
| JWT Property Management Ltd | Administrative & support | 2022 |
| K & M Motor Services Ltd | Wholesale & retail | 2017 |
| K & SP Consultancy Limited | Professional & scientific | 2014 |
| K Mcnaught Consulting Ltd | Information & communication | 2018 |
| K&C Construct Ltd | Construction | 2025 |
| K.M.M.C. Limited | Real estate | 1988 |
| K2M Pro Homes Limited | Real estate | 2021 |
| K9 Training Academy (Oxford) Limited | Professional & scientific | 2022 |
| Kacey Relocation Ltd | Hospitality | 2017 |
| KAD (Ckaf) Ltd | Hospitality | 2020 |
| Kadox International PLC | Transport & logistics | 1991 |
| Karma Solutions Limited | Information & communication | 2016 |
| Katebo Ltd | Administrative & support | 2017 |
| KAY London Ltd | Arts & recreation | 2013 |
| KCJ Training and Employment Solutions (Oxfordshire) Limited | Administrative & support | 2020 |
| Kearsley Airways (Holdings) Limited | Manufacturing | 1990 |
| Kelly House Management Company (Letcombe Regis) Limited | Households | 1988 |
| Kelly Management Ltd | Real estate | 2021 |
| Kenny Scaffolding Limited | Construction | 2025 |
| Kent's Services Limited | Other services | 2025 |
| Kersley-Rooke Ltd | Administrative & support | 2022 |
| Kessel Advisory Limited | Professional & scientific | 2025 |
| Kestrel Consulting Limited | Professional & scientific | 2010 |
| Ketevshn Ltd | Health & social care | 2015 |
| Kettle Studio Limited | Professional & scientific | 2012 |
| Kevin Taxi Ltd | Transport & logistics | 2026 |
| Kigo Logistics Limited | Transport & logistics | 2025 |
| Kinect Solutions International Limited | Information & communication | 2017 |
| Kingfisher House Rentals Ltd | Real estate | 2020 |
| Kingsgrove Accounting Ltd | Professional & scientific | 2025 |
| Kingsgrove Community Hub | Real estate | 2022 |
| Kirckman Concert Society Limited | Arts & recreation | 1963 |
| Kirkland C & C Limited | Wholesale & retail | 2024 |
| Kitcheno Limited | | 1992 |
| Kivist Joinery Limited | Construction | 2020 |
| KK Cappuccino & Baguette Bar Limited | Hospitality | 2004 |
| KK London (Designs & Fashion) Limited | Professional & scientific | 2020 |
| Klinrx Digital Health Limited | Information & communication | 2026 |
| Knowledge & Impact Strategy Services Ltd | Information & communication | 2018 |
| Konexis Ltd | Information & communication | 2024 |
| Kukri Design Limited | Professional & scientific | 1995 |
| Kunle Lonii Limited | Wholesale & retail | 2025 |
| Kvma Ltd | Construction | 2020 |
| Kvmg Properties Ltd | Real estate | 2023 |
| Kvmg Solutions Ltd | Information & communication | 2024 |
| L&P Works Ltd | Wholesale & retail | 2025 |
| L'Escargots UK Ltd | Agriculture & fishing | 2024 |
| LA Mahasneh Ltd | Health & social care | 2022 |
| Lakefield Capital Limited | Administrative & support | 2021 |
| Lambda Machines Limited | Information & communication | 2013 |
| Lambourn Valley Housing Trust | Administrative & support | 1995 |
| Lance Victor Properties Ltd | Real estate | 2024 |
| Lanes Equestrian Ltd | Agriculture & fishing | 2025 |
| Larkdown Environmental Limited | Professional & scientific | 2010 |
| Larkhill Farm Ltd | Agriculture & fishing | 2015 |
| Launchpad Delivery Limited | Information & communication | 2025 |
| Lbtw Development Ltd | Other services | 2024 |
| Legacy Double Glazing and Bifolds Ltd | Construction | 2019 |
| Lemniscate Services Limited | Information & communication | 2018 |
| Lemonade Life Ltd | Health & social care | 2020 |
| Leopard Business Solutions Limited | Information & communication | 2003 |
| Lester Lettings Limited | Real estate | 2023 |
| Letcombe Bowers Management Company Limited | Households | 2021 |
| Letcombe Greyhound Limited | Hospitality | 2012 |
| Letcombe Mews Residents Company Limited | Households | 2007 |
| Levels Social Media and Marketing Limited | Professional & scientific | 2026 |