Onyekuru spent last season on loan at the club from Olympiakos.
The Club have now opted to make his move permanent for a fee of €3.5m.
He has put pen to paper on a three-year deal to continue his sojourn in Turkey.
The 26-year-old enjoyed an impressive season with the Blues Lightnings, scoring eight goals and recording three assists in 30 games in the 2022-23 campaign.
Onyekuru has had stint at Anderlecht, Galatasaray, Monaco and Olympiakos in the past.
He made his Super Eagles debut against Togo in 2017.
He was also part of the Super Eagles squad for the 2019 Africa Nations Cup in Egypt.
Onyekuru scored his only goal for Nigeria against Seychelles in 2019 at the Stephen Keshi Stadium in Asaba.
Adana Demirspor finished fourth in the Turkish Super League last season with 69 points from 36 games.
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