The Herald of Free Enterprise was bound for the Port of Dover on 6 March 1987 when it capsized at Zeebrugge harbour in Belgium, killing 193 people.
A remembrance service was held at St Mary's Church in Dover, where a memorial window marks the tragedy.
Later, a rose garden was dedicated and flowers cast into the sea.
During the service, the names of the 193 people who died in the disaster were read out.
The service was attended by more than 250 bereaved family and friends, as well as some survivors of the tragedy.
The Bishop of Dover, the Right Reverend Trevor Willmott, said: "Although time has passed, the scars from that day, physical, emotional and spiritual, will remain until the end of our lives."
The congregation was given stars on which to write messages. They will be transcribed into a book of remembrance.
Also at the service was the Reverend Ken Martin, from Felixstowe, Suffolk, who was the first chaplain to arrive at the Naval Station at Zeebrugge.
He said: "When I arrived there, I met a man who had lost his wife and son. The whole thing is as fresh today as it was back then. It was a very sad occasion and I can't believe it was 25 years ago."
The memorial garden on the seafront at Dover was created to mark the anniversary, with 25 white roses.
Later the garden was dedicated and floral tributes cast from the Prince of Wales pier in Dover to remember those who died.
Bereaved families and survivors of the Zeebrugge ferry disaster gathered at a memorial service in Kent to mark its 25th anniversary.