| Speedyplumb Ltd | Construction | 2022 |
| Speirs Carpentry Contractors Limited | Construction | 2015 |
| Spencer Court ( Eastbourne) Residents RTM Company Limited | Households | 2026 |
| Spencer House Management (Eastbourne) Limited | Households | 1975 |
| Spic & Span Construction Cleaning Ltd | Administrative & support | 2016 |
| Spice Raja Ltd | Hospitality | 2026 |
| Spiddal Properties Ltd | Real estate | 2026 |
| Splodge Teddies LLP | | 2024 |
| Sporting Talent (Operations) Limited | Professional & scientific | 2020 |
| Sporting Talent Ltd | Professional & scientific | 2020 |
| Sportitude Ltd | Education | 2016 |
| Sports Education Solutions UK Ltd | Education | 2018 |
| Sportswise Limited | Health & social care | 1997 |
| Spotless Commercial East Sussex Ltd | Administrative & support | 2025 |
| Spraysmith Ltd | Manufacturing | 2006 |
| Spraystore Limited | Wholesale & retail | 2009 |
| Sprint Property Services Ltd | Construction | 2021 |
| Spsp Property Ltd | Real estate | 2019 |
| Square Eyes Films Limited | Information & communication | 2014 |
| SR Dental Limited | Health & social care | 2020 |
| SR Nutrition Limited | Other services | 2019 |
| SRH Catering Kitchen Ltd | Hospitality | 2022 |
| SRI SRI Care Limited | Health & social care | 2024 |
| SS Scientific Limited | Manufacturing | 1996 |
| Ssaf Properties Limited | Real estate | 2024 |
| SSC Building Services Ltd | Professional & scientific | 2019 |
| Ssekyanzi Ltd | Health & social care | 2015 |
| SSK Windows Ltd | Construction | 2025 |
| ST Annes Property (Eastbourne) Ltd | Professional & scientific | 2019 |
| ST Brelades Flat Owners RTM Company Limited | Households | 2014 |
| ST James Bookkeeping Limited | Professional & scientific | 2014 |
| ST James Events Ltd | Hospitality | 2016 |
| ST John's House (2024) Ltd | Households | 2024 |
| ST Johns House RTM Company Limited | Households | 2023 |
| ST Mary's Hotel Ltd | Hospitality | 2015 |
| ST Michael's Care Homes Limited | Health & social care | 2003 |
| ST Rode Property Management Limited | Households | 2000 |
| ST Roger Limited | Real estate | 2022 |
| ST Sign Installations Ltd | Construction | 2025 |
| ST Sussex Estates Ltd | Real estate | 2026 |
| ST Sussex Ltd | Wholesale & retail | 2025 |
| ST Wilfrid's Hospice (Eastbourne) | Health & social care | 1981 |
| ST Wilfrid's Hospice Eastbourne Trading Company Limited | Wholesale & retail | 1987 |
| ST. Demiana Hotel Ltd | Hospitality | 2017 |
| ST. John's Limited | Households | 1991 |
| ST. John's Street Limited | Real estate | 1996 |
| ST. Rita's Residents Association (Eastbourne) Limited | Households | 1994 |
| St.Ann's Court (Pevensey Bay) Limited | Households | 1969 |
| STA Partners Ltd | Wholesale & retail | 2021 |
| Stable Holdings Ltd | Real estate | 2015 |
| Stacey Adams Therapy Ltd | Health & social care | 2020 |
| Stackdev Ltd | Information & communication | 2022 |
| Stade Events CIC | Hospitality | 2024 |
| Stafford House (Eastbourne) Limited | Households | 1992 |
| STAGE3 Ltd | Administrative & support | 2023 |
| Stakeholder Limited | Information & communication | 2017 |
| Stallion Clothing Ltd | Wholesale & retail | 2013 |
| Stamford Carpentry (South East) Ltd | Construction | 2013 |
| Stanbridge Grab Services Ltd | Transport & logistics | 2022 |
| Stancrest Limited | Wholesale & retail | 2008 |
| Stancrest Stacked Limited | Hospitality | 2018 |
| Stand Together Stand Easy CIC | Health & social care | 2022 |
| Stand UP Media Ltd | Professional & scientific | 2021 |
| Standard Claim Ltd | Wholesale & retail | 2010 |
| Standset Limited | Professional & scientific | 1990 |
| Stanmer House (Eastbourne) Limited | Households | 2002 |
| Stanton Cottages Ltd | Real estate | 2022 |
| Stanton Prior House Limited | Real estate | 1990 |
| Staples & Sons Ltd | Construction | 2015 |
| Star Choice Windows Limited | Construction | 2017 |
| Star Court Management Limited | Households | 2018 |
| Star Paladin Productions Ltd | Arts & recreation | 2023 |
| Star Trading Estate Management Limited | Real estate | 2017 |
| Stark Investments (SE) Ltd | Construction | 2021 |
| Starshine Music Limited | Information & communication | 2003 |
| Start Communications Group Ltd | Information & communication | 2020 |
| Starting Grid Limited | Arts & recreation | 2005 |
| Static Consultants Limited | Professional & scientific | 2013 |
| Station Road Garage Services Limited | Manufacturing | 2024 |
| Status Barbers Ltd | Other services | 2026 |
| Staveley Mead Residents Limited | Households | 2022 |
| Staycation Lodge Homes Limited | Real estate | 2023 |
| Staycation Quarters Limited | Real estate | 2021 |
| Stech Experts Ltd | Information & communication | 2022 |
| Steel City Surgical Limited | Health & social care | 2020 |
| Steevenson Dental Limited | Health & social care | 2023 |
| Steffin Property Ltd | Real estate | 2015 |
| Stein Murcar Limited | Wholesale & retail | 2022 |
| Stelhan Limited | Real estate | 2018 |
| Stellar Partners Limited | Professional & scientific | 2020 |
| Stellar Pictures Ltd | Information & communication | 2021 |
| Stem Futures LLP | | 2023 |
| Stenhouse Enterprises Limited | Wholesale & retail | 2019 |
| Stenning Roofers Limited | Construction | 2026 |
| Stenroy Limited | Information & communication | 1985 |
| Stenza UK Limited | Real estate | 2014 |
| Step by Step Children's Nursery Ltd | Other services | 2016 |
| Step by Step Forest School Ltd | Health & social care | 2023 |
| Step by Step Property Co. Ltd | Real estate | 2026 |
| Step One Fashions Limited | Wholesale & retail | 2014 |