| Heritage Park (Sutton Courtenay) Residents Management Company Limited | Households | 2016 |
| Heritage Properties (Oxford) Limited | Real estate | 1993 |
| Hermosa Gardens Ltd | Administrative & support | 2022 |
| Heroes Scaffolding Ltd | Construction | 2020 |
| Herring Homes Designer/Constructors Limited | Construction | 2007 |
| Heslop Limited | Real estate | 2005 |
| Hesti Bili Tech Ltd | Wholesale & retail | 2026 |
| Hevin Hair Salon Ltd | Other services | 2016 |
| Hexin Group UK Ltd | Wholesale & retail | 2025 |
| HG Premier Property Investments Limited | Real estate | 2015 |
| HH Jones (Emsworth) Limited | Real estate | 2023 |
| Hibiscus (Oxford) Limited | Health & social care | 2017 |
| Hibt Limited | Education | 2004 |
| Hidenda Legal LLP | | 2020 |
| Hidenda Tax Limited | Professional & scientific | 2020 |
| Higgledy Piggledy Ziggy Ltd | Professional & scientific | 2025 |
| High Fade Music Limited | Other services | 2023 |
| High Hazard Management Ltd | Professional & scientific | 2020 |
| High Level Software Ltd | Information & communication | 2013 |
| High Performance Polymer Ltd | Wholesale & retail | 2021 |
| High Revs Studios Ltd | Wholesale & retail | 2020 |
| Highland Systems Ltd | Wholesale & retail | 2025 |
| Hilbro Rock Ltd | Wholesale & retail | 2021 |
| Hill & Weatherall Ltd | Construction | 2023 |
| Hills of Corby Hill Limited | Wholesale & retail | 1975 |
| Hills of Lakeland Limited | Wholesale & retail | 1980 |
| Hillscan Limited | Professional & scientific | 1990 |
| Hillside Lifestyles Ltd | Construction | 2025 |
| Hilway Limited | Transport & logistics | 2025 |
| Hinkins Langham Consultancy Limited | Professional & scientific | 2020 |
| Hiper Energy Systems Ltd | Information & communication | 2025 |
| Hirstwood and Fenwick Limited | Manufacturing | 2026 |
| Hitachi High-Tech Analytical Science Limited | Manufacturing | 2017 |
| HJ Restaurants Ltd | Hospitality | 2025 |
| HK Activities | Education | 1999 |
| Hoch Group Limited | Financial services | 2021 |
| HOI Wong Restaurant Limited | Hospitality | 2025 |
| Holgate Trading Ltd | Wholesale & retail | 2009 |
| Holistic Help Limited | Health & social care | 2026 |
| Hollie Doyle Ltd | Arts & recreation | 2018 |
| Holly India Ashby Ltd | Manufacturing | 2020 |
| Hollygog Events Ltd | Hospitality | 2024 |
| Homerun UK Ltd | Information & communication | 2014 |
| Honey Drops Ltd | Real estate | 2017 |
| Honey Housing Ltd | Real estate | 2020 |
| Hoodwinked Ltd | Wholesale & retail | 2022 |
| Hook Digital Ltd | Administrative & support | 2022 |
| Hooke's Homes Developments Ltd | Construction | 2022 |
| Hopgoods (Electrical) Limited | Construction | 1972 |
| Hopping Bunnies Ltd | Wholesale & retail | 2022 |
| Horse Events Limited | Arts & recreation | 2014 |
| Horsepower Factory Limited | Wholesale & retail | 2019 |
| Horspath Estates Limited | Real estate | 2000 |
| Hoshang Top Barber Ltd | Other services | 2026 |
| Houndstooth Publishing Limited | Information & communication | 2019 |
| House of Bull Music Group Ltd | Administrative & support | 2025 |
| House of Pickle Limited | Wholesale & retail | 2023 |
| House Ready Ltd | Administrative & support | 2023 |
| House Ready Ultimate Limited | Administrative & support | 2024 |
| HRON1 Ltd | Information & communication | 2017 |
| HRON2 Investments Ltd | Financial services | 2017 |
| Hugomangos Ltd | Hospitality | 2024 |
| Hulo Ltd | Agriculture & fishing | 2025 |
| Humb Group Limited | Wholesale & retail | 2020 |
| Humb Technologies Limited | Information & communication | 2024 |
| Humble and Preserved Ltd | Information & communication | 2022 |
| Hunting Dragons Consulting Ltd | Professional & scientific | 2019 |
| Huntinglands Limited | Agriculture & fishing | 1991 |
| Hunts Cleaning Limited | Administrative & support | 2005 |
| Hurley Motors LLP | | 2025 |
| Husted Consultancy Ltd | Professional & scientific | 2021 |
| Hutton Engineering (Precision) Limited | Manufacturing | 1999 |
| Hybrid Biosystems Limited | Health & social care | 1997 |
| Hybrid Car Care Ltd | Wholesale & retail | 2019 |
| Hyder Smith Property Management Limited | Real estate | 2019 |
| Hypha Discovery Limited | Professional & scientific | 2004 |
| I & S Goodenough Limited | Construction | 2004 |
| I P Baris Communications Limited | Professional & scientific | 2019 |
| I-Hav Ltd | Other services | 2021 |
| I2D Limited | Manufacturing | 2003 |
| Iambic Innovation Limited | Professional & scientific | 2000 |
| IAN Lawrence Limited | Arts & recreation | 2006 |
| Ibex England Ltd | Wholesale & retail | 2020 |
| Ibos Association Limited | Other services | 1999 |
| IBOX2GO Ltd | Transport & logistics | 2024 |
| Ibuild Oxford Ltd | Construction | 2020 |
| Iceni Property Asset Management (UK) Limited | Real estate | 2018 |
| Iceni Property Holdings Limited | Professional & scientific | 2023 |
| ID88 Ltd | Professional & scientific | 2022 |
| Ideal Flooring (Oxford) Limited | Construction | 2008 |
| Ifield Estates Limited | Administrative & support | 2005 |
| IG Innovations Limited | Professional & scientific | 2010 |
| IG3 Limited | Information & communication | 2010 |
| Iggwell Limited | Transport & logistics | 2021 |
| Ignite Capital Solutions Ltd | Real estate | 2023 |
| Imightby Ltd | Arts & recreation | 2023 |
| IML (Inspire Medilaw) Limited | Education | 2025 |
| Immunocore Holdings PLC | Financial services | 2021 |
| Immunocore Limited | Professional & scientific | 2007 |
| Immunocore Nominees Limited | Other services | 2017 |