Nicky Mohan, Rob Matthews, Lee Philpott and Mike Price have all been told be manager Jan Molby that they are surplus to requirements.
The news comes just a few days after the release of Theo Whitmore, Ian Goodison, Jason van Blerk, Adrian Caceres and Rodney Rowe.
Molby (pictured) has also told youngster Ben Morley that his contract will not be renewed.
"I've spoken individually to every player and have informed four of those that I don't see them being part of the future at Hull City," said Molby.
"Nicky, Rob, Lee and Mike are all available, as is Ben Morley who's probably a bit unlucky to be released.
"I know Mike is a young player but he's never really been anywhere near the first team over the past season and I don't see that situation changing next season.
"In the case of Nicky I just feel that we need a big, dominant centre half and if I succeed in bringing one in over the summer then that would give us six at the club.
"With Nicky being at the stage of his career that he's at, he needs to be playing football and I can't guarantee that he'll be doing that for us next season.
"So we've given him - and the other four guys - a chance to go out and try and find themselves a new club.
"Obviously with them being under contract there is no guarantee that they won't be here come July 4th when we report back for pre-season training.
"I accept that and if it turns out to be the case they'll have the chance to impress me but as things stand today I've made decisions and that's the way it is in football.
"They're the wrong side of 30 if you like and I don't want our squad players or substitutes to be that.
"I want them to be younger, up and coming players. These guys were brought in to play first team football but I can't really see that happening so there's no point in keeping them.
"As for the rest of the squad, they've all been told that they're part of what we're trying to do.
"Certainly nothing will change until we come back in on July 4th and a lot will depend on who I bring in and what positions they play in.
"I suppose over the course of time some players may become unhappy and could want to leave but we'll to wait and see on that score."
