The ward, which is in the Thomas Kemp Tower, provides specialist care for surgical patients.
The hospital trust said it is part of an ongoing investment programme which is improving and developing services across the trust.
The clinical team were joined by Marianne Griffiths, chief executive of Brighton and Sussex University Hospitals NHS Trust (BSUH), and Alan McCarthy, BSUH chairman, for a ribbon cutting ceremony.
BSUH chief executive Mrs Griffiths said: “Opening this ward will increase the number of beds we have, which will allow us to treat patients more quickly and help ease pressure on our busy Emergency Departments. More importantly this will help us improve the experience of our patients by ensuring they are in the right place to receive the most appropriate specialist care.
"A huge effort has been put in by everyone involved with this project to make the opening of this ward possible. I would like to thank each and every person for the part they have played. This makes a real difference to the quality of care our patients receive and to our staff who work so hard to deliver outstanding care."