Mark Lock, Darren Edwards, Colin Noon, Pablo Bouza, Martin Schusterman, John Holtby, Mike Aspinall, Tom Rock, James Parkes, Andy Rock, Richard Vasey, Tom Whittaker, Max Lewis and Michael Cusack are the departing players.
Leeds director of rugby Stuart Lancaster said: "All of these players have given outstanding service to the club.
"The majority of them have been with us for the past two years and joined the club at a difficult time in our history.
"Their dedication and commitment went a long way to rebuilding the team and we will always be grateful for that."
However, full-back Leigh Hinton, 29, and centre Jonny Hepworth, 25, have agreed new one-year and two-year deals respectively.
Lancaster said: "Both Leigh and Jonny were important players for us last season.
"They will be stronger from the experience of having performed at the highest level in the Premiership this season."