| Hilltop Sessions CIC | Arts & recreation | 2022 |
| Hillyfield Medical Limited | Health & social care | 2022 |
| Hilt Agency Ltd | Professional & scientific | 2009 |
| Hiscox Property Ltd | Real estate | 2016 |
| History Mysteries Ltd | Manufacturing | 2020 |
| Hiwin Services Ltd | Administrative & support | 2014 |
| HJF Enterprise Limited | Professional & scientific | 2013 |
| HMG (Brighton) Limited | Households | 1999 |
| Hmsoftware Limited | Information & communication | 2019 |
| Hobbes and Locke Ltd | Wholesale & retail | 2022 |
| Holdemhigh Limited | Other services | 2014 |
| Holly Farm Buxted Limited | Agriculture & fishing | 2015 |
| Home Comforts Community Care Limited | Health & social care | 1999 |
| Home Heat (Clayhill) Limited | Construction | 1998 |
| Honeygrove (Swaylands) Limited | Professional & scientific | 1999 |
| Hoods Croft Stays LLP | | 2025 |
| Hook Strategy Limited | Professional & scientific | 2019 |
| Hornbeams Holdings Limited | Construction | 2024 |
| Horsman Solicitors Ltd | Professional & scientific | 2002 |
| Hospitality Management Services Associates Limited | Hospitality | 2024 |
| Hounsfield Health Limited | Wholesale & retail | 2026 |
| House of Chatty Ltd | Wholesale & retail | 2026 |
| House of Halcyon Ltd | Health & social care | 2019 |
| Housedean Farm Campsite Limited | Hospitality | 2014 |
| HOW Many Beans Make Five Limited | Manufacturing | 2004 |
| Howard Eaton Lighting Limited | Manufacturing | 1988 |
| HOY Consulting Limited | Information & communication | 2006 |
| Hskr Ltd | Construction | 2022 |
| Hub Agency Ltd | Information & communication | 2020 |
| Human + Nature (Lewes) Limited | Construction | 2020 |
| Human Nature (Hethel) Limited | Construction | 2024 |
| Human Nature (Horam) Ltd | Construction | 2023 |
| Human Nature (Places) Limited | Professional & scientific | 2007 |
| Human Nature Places Foundation | Other services | 2022 |
| Hummingbird Art Consultancy Ltd | Professional & scientific | 2024 |
| Hunt & Taylor Ltd | Construction | 2024 |
| Hunter Gather Cook Limited | Education | 2015 |
| Hurlock Design Limited | Information & communication | 2002 |
| Hutchinson Management Ltd | Real estate | 2022 |
| Hutty Luck Associates Ltd | Professional & scientific | 2026 |
| Hyatt Associates Limited | Arts & recreation | 2020 |
| I Timber Ltd | Manufacturing | 2014 |
| IAN Budden Ltd | Information & communication | 2024 |
| Ideas Unfolding Ltd | Information & communication | 2021 |
| Idhi Consulting Ltd | Professional & scientific | 2023 |
| Iford Estate Limited | Financial services | 2023 |
| IH4 ICT Limited | Information & communication | 2009 |
| IJT Limited | Construction | 2019 |
| ILO Head Spa Ltd | Other services | 2025 |
| Imagemap Ltd | Information & communication | 2024 |
| Imar Real Estate Ltd. | Real estate | 2008 |
| Imdex UK Ltd | Administrative & support | 2008 |
| Imitate Limited | Arts & recreation | 2010 |
| Imli Lewes Restaurant Ltd | Hospitality | 2025 |
| Imogen Perreau Studio Ltd | Administrative & support | 2024 |
| Impact Chain Ltd | Information & communication | 2026 |
| Impact Sustainability Ltd | Professional & scientific | 2019 |
| Imperial Framing and Construction Limited | Construction | 2025 |
| Imperial Framing Limited | Construction | 2012 |
| IN ANY Event Limited | Real estate | 2000 |
| IN Roads Productions Ltd | Arts & recreation | 2018 |
| IN Studio Limited | Information & communication | 2020 |
| In-Align Ltd | Administrative & support | 2010 |
| Inbox Cleanser Ltd | Information & communication | 2026 |
| Independent Neuroscience Services Inss Limited | Professional & scientific | 2016 |
| Independent Utility Distributors Ltd. | Wholesale & retail | 2007 |
| Indie Mamma Limited | Wholesale & retail | 2019 |
| Industrial Construction (Sussex) Limited | Construction | 1992 |
| Infinity Accounts Services Ltd | Professional & scientific | 2026 |
| Infograph Ltd. | Information & communication | 2023 |
| Infotech 24 7 Limited | Information & communication | 2002 |
| Infraviva Limited | Professional & scientific | 2011 |
| Ingenious Design Limited | Professional & scientific | 2009 |
| Inglis Hall Property Ltd | Households | 2023 |
| Innervision Health and Safety Limited | Other services | 2021 |
| Innovit Solutions Ltd | Information & communication | 2025 |
| Inpulsa Ltd | Manufacturing | 2020 |
| Insiders Guide to the Galaxy LLC | | 2012 |
| Insight Atlas Limited | Information & communication | 2023 |
| Intec Export Intelligence Limited | Professional & scientific | 2002 |
| Integrated Heat Exchange Ltd | Professional & scientific | 2020 |
| International Iron Metallics Association Limited | Administrative & support | 2010 |
| Interpreters Direct Limited | Extraterritorial | 2003 |
| Interventus Limited | Professional & scientific | 2010 |
| Intrepid Spirits UK Limited | Manufacturing | 2014 |
| Invent & Create Ltd | Manufacturing | 2019 |
| Invisible Typewriter Limited | Manufacturing | 2024 |
| Ioptimal Ltd | Information & communication | 2010 |
| Ipsofacto Investor.Com Limited | Financial services | 2011 |
| Irresistible Entertainment Limited | Arts & recreation | 2004 |
| Irving International Limited | Professional & scientific | 2004 |
| Isolvia Ltd | Wholesale & retail | 2022 |
| IT Socks to BE Lonely Sometimes Limited | Other services | 2017 |
| Itchy Feet Homecoming Limited | Arts & recreation | 2015 |
| Iucn SSC PSG Section on Small Apes Limited | Professional & scientific | 2024 |
| Ixopo Ltd | Financial services | 2025 |
| J Parnaby Groundworks Ltd | Construction | 2019 |
| J RAK Carpentry Limited | Manufacturing | 2015 |
| J&L Health and Wellbeing Ltd | Health & social care | 2024 |
| J&R Woodcraft Ltd | Manufacturing | 2022 |