Adriaan Strauss, Trevor Nyakane, Pieter Labuschagne and Jamba Ulengo have all left the Cheetahs to join the Bulls.
Forwards Strauss, Nyakane and Labuschagne will link up with their new team on November 1 while winger Ulengo has already started training with the Blue Bulls ahead of their Currie Cup campaign.
The moves deal a huge blow to the Bloemfontein-based Cheetahs, with the loss of South Africa hooker Strauss particularly tough to take as he had spent recent seasons as their captain.
Strauss is making a return to Loftus Versfeld, where he made his Super Rugby debut and won a share of the Currie Cup title in 2006.
He and international prop Nyakane have signed with the Bulls until the end of 2017 with Labuschagne - also a Springboks squad member - and sevens speedster Ulengo have signed on for two seasons.
Bulls high performance manager Xander Janse van Rensburg said: "We are pretty excited about these signings as all of them are proven performers at the highest level.
"These players are all very keen to share in our vision of becoming the number one team in both Super Rugby and Currie Cup and to help us achieving those milestones.
"These are important and significant signings, as they show that we are still seen as a pathway to international honours and the winning of tournaments and cups by established, as well as emerging players.
"The decision of Adriaan to join us will not also add depth to our hooking position, but with his extensive role as captain, will also provide fantastic leadership and solid international experience."