| Hcoffee Ltd | Hospitality | 2026 |
| Health Claims Bureau Limited | Professional & scientific | 1993 |
| Healthcom Partners Limited | Health & social care | 2002 |
| HEALTHYFOOD4ME Limited | Wholesale & retail | 2012 |
| Heddon Consulting Limited | Information & communication | 2016 |
| Hedges & Ogilvie | | 1991 |
| Helisafe-Surveyor Ltd | Information & communication | 2026 |
| Helping Hands for Japan | Other services | 2011 |
| Helptobuy Ltd | Wholesale & retail | 2025 |
| Hendred Holdings Ltd | Professional & scientific | 2026 |
| Hendred Oak Ltd | Real estate | 2019 |
| Hendred Sports Club Trading Limited | Hospitality | 2019 |
| Hendred Vineyard LLP | | 2014 |
| Hermes Chemical Limited | Manufacturing | 2014 |
| Heros | Agriculture & fishing | 2006 |
| Hetherington Estates Limited | Real estate | 1998 |
| Hexagon Webworks Ltd | Information & communication | 2012 |
| Hick's Roofing Limited | Construction | 2024 |
| Higgs and Webb Brick and Stone Limited | Construction | 2015 |
| Highmoor Nursery School Limited | Education | 2004 |
| Highworth Skip Hire Limited | Water & waste | 2019 |
| Hillsdon and Sons Limited | Construction | 1983 |
| Hillsdon Construction Limited | Extraterritorial | 2002 |
| Himalayan Crafts Ltd. | Manufacturing | 2014 |
| Holy King Clothing Ltd | Wholesale & retail | 2025 |
| Home Counties Bailiff Services Limited | Administrative & support | 2018 |
| Home Farm (Charlton) Estates Limited | Agriculture & fishing | 1971 |
| Home Farm (Charlton) Holdings Limited | Financial services | 2021 |
| Home Farm Salon Limited | Other services | 2015 |
| Home Sweet Care Ltd | Health & social care | 2024 |
| Home-School Tutoring (Oxfordshire and Berkshire) Limited | Education | 2007 |
| Hoptimist Brewery Ltd | Extraterritorial | 2023 |
| Horse Kick Cider Ltd | Manufacturing | 2016 |
| Hot Stepper Contracts Ltd | Construction | 1999 |
| Hotspot Mobiles Ltd | Wholesale & retail | 2018 |
| Howard Enterprises Ltd | Construction | 2002 |
| Howell & Collins Limited | Construction | 2017 |
| Howme Digital Limited | Other services | 2019 |
| Howme Entertainment Limited | Other services | 2019 |
| Howme Group Limited | Financial services | 2019 |
| Howme Investments Limited | Real estate | 2019 |
| Hpld Limited | Administrative & support | 2026 |
| Hubbard Engineering Ltd | Professional & scientific | 2018 |
| Humble Havens Limited | Real estate | 2020 |
| Hummels Brickwork Ltd | Construction | 2014 |
| HV Spectre Ltd | Information & communication | 2024 |
| Hyggeiavantage Ltd | Professional & scientific | 2026 |
| Hypable (UK) Limited | Information & communication | 2018 |
| Hype Gorilla Ltd | Information & communication | 2015 |
| I Environmental Technologies Limited | Manufacturing | 2009 |
| I.Scaff Safety Netting & Access Solutions Ltd | Construction | 2020 |
| I2SI Limited | Professional & scientific | 2012 |
| Iain Rodger Consulting Ltd | Professional & scientific | 2024 |
| Iaitam Europe Limited | Other services | 2011 |
| Iaso Communications Ltd | Professional & scientific | 2015 |
| Ibase Group Limited | Information & communication | 2005 |
| Ibase Systems Limited | Information & communication | 1999 |
| IBP Consulting Limited | Information & communication | 2015 |
| Ibrahim Services Ltd | Wholesale & retail | 2020 |
| Ichorbio Ltd | Professional & scientific | 2019 |
| Iease Limited | Construction | 2009 |
| Ilexanna Limited | Real estate | 2013 |
| IM Mechanical Consultant Limited | Professional & scientific | 2024 |
| Imagination Workshop Ltd | Arts & recreation | 2015 |
| Imani Care Solutions Ltd | Health & social care | 2025 |
| Improving Generational Outcomes C.I.C. | Education | 2017 |
| IN Fine Spirits Catering and Events Ltd | Other services | 2019 |
| Infiniscape Limited | Professional & scientific | 2023 |
| Innovation Edge Ltd | Professional & scientific | 2024 |
| Inochi Ventures LLP | | 2008 |
| Inspiritus Health Limited | Professional & scientific | 2022 |
| International Brand Technologies Limited | Professional & scientific | 2020 |
| Inua Consulting Limited | Professional & scientific | 2025 |
| Invest in Oxford Ltd | Real estate | 2022 |
| IQ Health Supplements Ltd | Manufacturing | 2025 |
| Iris Properties Oxford Ltd | Households | 2025 |
| Iron Hippo Ltd | Wholesale & retail | 2024 |
| Ironbeast Wear Limited | Manufacturing | 2023 |
| Irun Limited | Professional & scientific | 2010 |
| Irun Systems Ltd | Information & communication | 2012 |
| IS Remedial Plumbing Services Ltd | Households | 2026 |
| Isho Ltd | Professional & scientific | 2023 |
| Isis Scaffolding Limited | Construction | 1986 |
| Isobel Davis Ltd | Professional & scientific | 2023 |
| Istunning Visuals Ltd | Wholesale & retail | 2025 |
| IT Smith Properties Limited | Real estate | 2021 |
| It's Sugar! Ltd | Wholesale & retail | 2024 |
| Itek Consultancy Limited | Information & communication | 2024 |
| Ivivo Limited | Professional & scientific | 2020 |
| IX Academics Limited | Education | 2010 |
| J Godfrey & SON Funeral Services Limited | Other services | 2014 |
| J Jenkin & Associates Limited | Professional & scientific | 2016 |
| J&Ak Networks Ltd | Information & communication | 2015 |
| J&C Forestry Ltd | Agriculture & fishing | 2025 |
| J. Archard Contracting Limited | Manufacturing | 2018 |
| J.M Welding & Fabrication Ltd | Manufacturing | 2022 |
| J2QS Limited | Professional & scientific | 2018 |
| Jackie Waller Locum Limited | Professional & scientific | 2022 |
| James Harris Investigations Limited | Administrative & support | 1996 |
| James Ross & Co Limited | Professional & scientific | 2014 |