Jon Macken, Darren Moore and Anderson De Silva have been told they are not in Barnsley manager Mark Robins' plans for next season.
Robins, who has begun talks with several potential summer recruits, will not be offering new contracts to the experienced trio, whose current deals are due to expire.
Striker Michael Coulson and midfielder Simon Heslop have also been released.
Barnsley have already offered improved terms to Daniel Bogdanovic, but the Malta international striker has yet to commit himself to Oakwell, while player of the year Hugo Colace is considering his new contract offer.
On-loan players Filipe Teixeira (West Brom), Carl Dickinson (Stoke) and Ryan Shotton (Stoke) have all returned to their parent clubs.