Xcalibar Dungeon was brought by landlords Tony Court and Sue Rossiter in 1989, when it was known as the Crown and Sceptre.
The watering hole in Bevois Valley Road will hold a fancy dress party tonight to celebrate and Sue and Tony are calling on old regulars to come back and raise their glasses.
The couple only bought the Crown and Sceptre, which first opened in 1957, after they quit their previous jobs as postal workers.
Sue, 60, said: “When we walked into the place we saw there was someone drinking here and we thought this is the one for us.”
The pub has been well known for its rock music, and the ‘Dungeon’ part of its name was created after they converted the cellar into a nightclub.
It also had a popular comedy club night that saw well-known comedians like Harry Hill and Dave Thompson headlining.
Now it is trying to move away slightly from its origins as a hideaway for rock fans and a refurbishment in July last year saw upstairs converted into a pub.
The party will be held from 9pm to 2am, and is free to attend before 10pm, after that it will cost £3.