The 31-year-old, who was earlier linked to Bursaspor, joins the Anatolian Star on a two-year contract with an option to renew for another year.
He spent last season on loan with UAE side Al Ahli Dubai from Chinese outfit Shanghai SIPG.
“It’s been a while we have been negotiating with the famous Asamoah Gyan and an agreement has been reached in the latest talk,” the club announced on their official website.
“Our club president Dr Erol Bedir, Gokhan Altıntas, Tuna Kaya and our club officials held a last meeting with Gyan in Istanbul where a 2-year (with an additional one-year renewable) contract was signed.
“Our president, Gyan and the club officials will move to Kayseri tonight.”
Gyan returns to Europe for the first time since leaving English club Sunderland in 2011.
From the Black Cats, the frontman joined Arabian outfit Al Ain, from where he later moved to Shanghai SIPG.
Before moving to England, he played for Rennes in France, Italian clubs Udinese and Modena as well as local outfit Liberty Professionals.
Kayserispor finished just a place above the relegation spot in the Turkish league last season.