The activity of electrocatalysts strongly depends on the number of active sites, which can be increased by downsizing electrocatalysts. Single-atom catalysts have attracted special attention due to atomic-scale active sites. However, it is a huge challenge to obtain atomic-scale CoO x catalysts. The Co-based metal-organic frameworks (MOFs) own atomically dispersed Co ions, which motivates to design a possible pathway to partially on-site transform these Co ions to active atomic-scale CoO x species, while reserving the highly porous features of MOFs. In this work, for the first time, the targeted on-site formation of atomic-scale CoO x species is realized in ZIF-67 by O 2 plasma. The abundant pores in ZIF-67 provide channels for O 2 plasma to activate the Co ions in MOFs to on-site produce atomic-scale CoO x species, which act as the active sites to catalyze the oxygen evolution reaction with an even better activity than RuO 2 .