WillGriff John, Latu Makaafi, Jarad Williams and Sean Scanlon have joined Sale, Coventry, Bedford and Nottingham respectively.
Utility back Sam Edgerley has accepted an offer to study for a Masters Degree in Modern Languages at the University of Oxford.
Prop Robin Hislop, hooker Harry Allen, locks Ed Falkingham and Dave Nolan, as well as former Australian international Beau Robinson have also departed Castle Park.
Knights director of rugby Clive Griffiths said: “I have written to each of the lads individually to thank them for their immense contribution and the way in which they have conducted themselves in their time at Castle Park.
“Some have been with us for a long time like Latu, a Club centurion, and WillGriff whilst others only for a season but all have brought plenty into our group and now move on to the next stage of their careers.
“Every year we have to go through this process and whilst it is sad, it is also pleasing to see the likes of WillGriff progress to the Premiership - like Will Hurrell did last year. We see it as part of our culture to develop players for the very top level so it’s a feather in the cap of Doncaster Knights.
“We wish them all every success in their future endeavours.”