| Seaoak Properties Limited | Real estate | 1992 |
| Seaview Holdings Limited | Real estate | 2004 |
| SEB Tech Limited | Information & communication | 2015 |
| Secure Windows Supplies | | 1998 |
| Select Gardens Limited | Administrative & support | 2003 |
| Semple IT Solutions Ltd | Information & communication | 2025 |
| Seven Sisters Electrical Ltd | Construction | 2020 |
| Shaftcase Limited | | 1987 |
| Shan Civil Engineering Consultants Limited | Construction | 2018 |
| Sharing Skills CIC | Professional & scientific | 2022 |
| Shaunywa Films Limited | Information & communication | 2003 |
| Sheep PEN Holdings Limited | Financial services | 2018 |
| Shelldean Limited | Water & waste | 2025 |
| Sheppards Removals and Clearances Ltd | Water & waste | 2025 |
| Shine Cosmetics Ltd | Wholesale & retail | 2022 |
| Shine Hair Limited | Other services | 2007 |
| Shoreline Accountants Ltd | Professional & scientific | 2011 |
| Shoreline Accounting Solutions Ltd | Administrative & support | 2015 |
| Shortcuts Barbers Seaford Ltd | Other services | 2025 |
| Shortlands Management Company Limited | Households | 1991 |
| SI Homes Ltd | Construction | 2013 |
| Signature Commercial Interiors Ltd | Construction | 2017 |
| Simmons Management Limited | Real estate | 2005 |
| Simply Spotless Limited | Administrative & support | 2016 |
| Sirimani Cloud Digital Ltd | Information & communication | 2020 |
| Sirimani Consulting Ltd | Information & communication | 2023 |
| Sirimani Services Ltd | Real estate | 2019 |
| SIXTEEN22 Ltd | Real estate | 2024 |
| SJS Engineering Services Ltd | Professional & scientific | 2015 |
| Skipperwatersportsandcafe Ltd | Health & social care | 2023 |
| Slava D Ltd | Transport & logistics | 2021 |
| Sloth and Glow Limited | Wholesale & retail | 2023 |
| Smallwood & Co Homes Ltd | Real estate | 2025 |
| Smart Kebabish Limited | Hospitality | 2026 |
| Smart Kitchen 2026 Limited | Hospitality | 2025 |
| Smilehaven Ltd | Health & social care | 2024 |
| Smith Renovation Ltd | Construction | 2018 |
| Soalsy Limited | Extraterritorial | 1996 |
| Soaring Penguin Ltd | Information & communication | 2004 |
| South Coast Management Services Ltd | Construction | 2011 |
| South Downs Software Ltd | Information & communication | 2025 |
| South East Mountain Biking Ltd | Arts & recreation | 2011 |
| Southdowns Physiotherapy (Newhaven) Ltd | Health & social care | 2021 |
| Southdowns Physiotherapy Limited | Health & social care | 2014 |
| Southern Alarm Systems Ltd | Other services | 1986 |
| Southern Counties Car Sales Limited | Real estate | 1995 |
| Space Plus Limited | Professional & scientific | 2023 |
| Spice Expert Limited | Hospitality | 2023 |
| Spice Meridian UK Limited | Wholesale & retail | 2025 |
| Splash Point Music Limited | Arts & recreation | 2005 |
| Sportorium Ltd | Construction | 2024 |
| Sportsfulminds Ltd | Education | 2025 |
| Springfield Park Gate Residents Management Company Ltd | Households | 2012 |
| Spur Hill Properties Limited | Households | 1993 |
| Squid Medical Limited | Health & social care | 2012 |
| SR Media Limited | Administrative & support | 2026 |
| ST. James' Trust (Seaford) | Health & social care | 2004 |
| ST. Johns Road (Seaford) Limited | Households | 1986 |
| Stafford House RTM Company Limited | Households | 2009 |
| Standen Court (East Grinstead) Management Company Limited | Households | 2003 |
| Staples Properties (Sussex) Ltd | Real estate | 2017 |
| Startpoint Recruitment Solutions Ltd | Administrative & support | 2025 |
| STE Group Ltd | Wholesale & retail | 2017 |
| Steamworks (Glynde) Limited | Hospitality | 2021 |
| Steamworks (Seaford) Limited | Extraterritorial | 2021 |
| Steer Change Ltd | Professional & scientific | 2026 |
| Steve Hodges Leadwork Ltd | Construction | 2014 |
| Stock Room (Seaford) Ltd | Wholesale & retail | 2016 |
| Stonemason Stoves Ltd | Construction | 2016 |
| Stoneway Construction Ltd | Construction | 2023 |
| Storm Event Services Limited | Other services | 2019 |
| Stoten & Waller Property Investments Ltd | Real estate | 2021 |
| Strange Logic Limited | Professional & scientific | 2017 |
| Strategic Edge Business Solutions Ltd | Administrative & support | 2025 |
| Strategic Health Research Limited | Health & social care | 2021 |
| Stratheden Residents Seaford Limited | Households | 1987 |
| STS Kitchens and Bathrooms Ltd | Construction | 2025 |
| Sussex Assistance Ltd | Manufacturing | 2016 |
| Sussex Bike Hire Limited | Administrative & support | 2022 |
| Sussex Boat Trips Ltd | Transport & logistics | 2020 |
| Sussex Brickwork & Plastering Ltd | Construction | 2012 |
| Sussex Business Coaching Limited | Professional & scientific | 2004 |
| Sussex Coast Accounting Ltd | Professional & scientific | 2026 |
| Sussex Glass Limited | Arts & recreation | 1992 |
| Sussex Grounds Maintenance Ltd | Administrative & support | 2013 |
| Sussex Health Clinical Advisory Services Limited | Manufacturing | 2026 |
| Sussex Heat Pumps Limited | Construction | 2018 |
| Sussex Housing Association Limited | Extraterritorial | 1994 |
| Sussex HR Services Limited | Real estate | 2010 |
| Sussex Human Resources Limited | Administrative & support | 2011 |
| Sussex Sea Salt Company Limited | Mining & quarrying | 2026 |
| Sutton Barn Community Club CIC | Education | 2022 |
| Sutton Drove Seaford Management Limited | Households | 2017 |
| Sutton Mews Seaford Management Limited | Real estate | 2016 |
| Swift Brothers Limited | Construction | 2006 |
| Sycamore Renovations Brighton Ltd | Construction | 2023 |
| Symposium Property Company Ltd | Real estate | 2009 |
| T&J Legacy Group Limited | Health & social care | 2025 |
| Tate Surveying Services Ltd | Other services | 2017 |
| Tayler Brown Limited | Administrative & support | 2025 |