Kōō (Nanboku-chō period)
, also romanized as Kō-ō, was a Japanese era name (年号, nengō, lit. year name) of the Northern Court during the Nanboku-chō period after Kakei and before Meitoku.  This period started in February 1389 and ended in March 1390.  The pretender in Kyoto was .  Go-Komatsu's Southern Court rival in Yoshino during this time was {{nihongo|Emperor Go-Kameyama|後亀山天皇|Go-Kameyama-tennō}}.