Leverkusen sit second in the Bundesliga and have bolstered their squad with the signing of the 20-year-old Ryu.
The forward, who starred for South Korea at the Under-20 World Cup in Turkey this year, will link up with compatriot Son Heung-Min at the BayArena.
Ryu completed a medical in Leverkusen on Wednesday and the club said he would join team-mates at a training camp in Portugal early next year.
Leverkusen also announced they had the option to buy Ryu at the end of his 12-month loan deal.
Ryu was regularly linked with a switch to Borussia Dortmund earlier this year, but a deal did not materialise.
Leverkusen are seven points behind runway Bundesliga leaders Bayern Munich and will play their last match of 2013 at struggling Werder Bremen on Saturday.
