Ryu recovered from playing her first five holes in three over to shoot a two-under second round and reach seven under at Royal Lytham & St Annes. Shiho Kuwaki trails by one stroke.
Ryu birdied the 18th to secure the outright lead. Jeeno Thitikul and Yealimi Noh share third at five under, while Nelly Korda is six strokes back.