Hiroshi Aoyama will quit Gresini's MotoGP squad at the end of 2011 to join Honda's factory World Superbike team alongside Jonathan Rea.
The 29-year-old Japanese rider won the final 250cc world championship with Scot Racing in 2009, before graduating to the premier class with the Interwetten Honda team, but his 2010 season was marred by a back-breaking shunt at Silverstone.
Aoyama has been largely overshadowed by teammate Marco Simoncelli in 2011, though the Italian has had access to the latest-spec HRC machinery.
"I have raced in MotoGP for the last couple of years and it has really been a great experience for me," said Aoyama. "I really want to thank Fausto Gresini and all the staff and technicians for this extraordinary period in my career. Now I have the opportunity to go to World Superbike with Honda and Ten Kate Racing and I'm very excited about this new challenge. I don't know very much about Superbike but I really hope to make a good job together with my new team."
Gresini said: "Our relationship with Hiroshi Aoyama is without doubt one of mutual esteem and respect and I hope that the times spent with Gresini has helped his career to grow in such a difficult category as MotoGP.
"Next season he will start a new adventure in World Superbikes. I would like to wish him all the very best and I hope he finds the determination and motivation to win."