He joins from the Chinese side Shanghai SIGP, who had loaned him to Al Ahli in the United Arab Emirates last season.
The 31-year-old ends a five-year absence from Europe after he left English club Sunderland in 2012.
Kayserispor have finished just one place above the relegation zone in the Turkish top flight for the last two seasons.
He is expected to help stabilise the team and make them a mid-table team with his huge profile and experience.
Asamoah Gyan is Ghana’s highest goal scorer with 51 goals, having notched his half-century against Ethiopia before netting in a friendly against the USA.
Join GhanaStar.com to receive daily email alerts of breaking news in Ghana. GhanaStar.com is your source for all Ghana News. Get the latest Ghana news, breaking news, sports, politics, entertainment and more about Ghana, Africa and beyond.
(Via: CitiFM Online Ghana)