The winger has signed a four-year deal with the Black Eagles after failing to make the grade in the Premier League.
Nkoudou moved from Marseille to Tottenham in 2016 but saw his first-team opportunities severely restricted.
Now he will look to relaunch his career in Turkey after leaving north London on Thursday.
"We have reached agreement with Turkish Super Lig side Beu015fiktau015f for the transfer of Georges-Kevin Nkoudou," Spurs confirmed on their official website.
"Having joined us from French side Marseille in 2016, the winger made 27 appearances in our colours, scoring once, and spent time on loan with Burnley and AS Monaco.