Supported metal catalysts with appropriate metal-support interactions (MSIs) hold a great promise for heterogeneous catalysis. However, ensuring tight immobilization of metal clusters/nanoparticles on the support while maximizing the exposure of surface active sites remains a huge challenge. Herein, we report an Ir/WO3 catalyst with a new enrooted-type MSI in which Ir clusters are, unprecedentedly, atomically enrooted into the WO3 lattice. The enrooted Ir atoms decrease the electron density of the constructed interface compared to the adhered (root-free) type, thereby achieving appropriate adsorption toward oxygen intermediates, ultimately leading to high activity and stability for oxygen evolution in acidic media. Importantly, this work provides a new enrooted-type supported metal catalyst, which endows suitable MSI and maximizes the exposure of surface active sites in contrast to the conventional adhered, embedded, and encapsulated types.