Proton-exchange membrane fuel cell and water electrolyzer (PEMFC and PEMWE) with high conversion efficiency and zero-carbon emission stand out as an attractive strategy for efficient conversion between hydrogen energy and renewable electricity. As a key component, efficient oxygen electrocatalyst for promoting sluggish reaction kinetics of oxygen reduction and evolution reaction (ORR and OER) under harsh operation conditions severely limited progress of these devices. Among various candidates, Pt-group (Pt, Ir, and Ru)-based electrocatalysts are still the most active ORR/OER catalysts. However, the scarcity, high cost, and questionable stability restrict the widespread applications and the commercialization of PEMWE/PEMFC. Progresses in synthesizing atomically dispersed single/multiple-atom catalysts (SACs/MACs) offer new opportunities to Pt-group ORR/OER catalysts owing to nearly 100% metal utilization and high catalytic activities. Extensive efforts have been continuously devoted to optimizing the local structure of Pt-group OER/ORR catalysts at atom-level for further enhancing stability and activity. In this review, universal synthesis methods to prepare Pt-group SACs are discussed first, highlighting crucial factors which affect the structure and catalytic performance. Afterward, advanced characterization techniques for directly confirming atomic dispersed metal atoms were introduced, including aberration-corrected high-angle-annular-dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy. Importantly, considerations for rational catalyst design and typical Pt-group SACs/MACs are summarized regarding the regulation strategy of atomically dispersed metal sites and various supports, and effects of metal–support interaction on the catalytic performance. Finally, key challenges and proposed perspectives for future development of atomically dispersed Pt-group oxygen electrocatalysts for fuel cell and electrolyzer are briefly discussed.