Pt-based multi-structured nanocatalysts such as alloy, core-shell, and surface Pt-rich nanoparticles have been exten-sively studied for hydrogen fuel cell applications, and their catalytic performances for oxygen reduction reactions have been signif-icantly upgraded for decades. These technical enhancements have resulted in Pt-based nanoarchitectures suitable for use in com-mercially available fuel cell systems. In addition, based on physical and electrochemical backgrounds for the basic catalyst nanoar-chitectures, novel catalyst designs with organic-inorganic hybrid concepts have been recently developed to more effectively im-prove the electrochemical reaction activities and durabilities. In this review, the typical class of Pt-based nanocatalysts are system-atically explained according to their compositions and structures, and emerging class of organic-inorganic hybrid catalyst designs are then intensively introduced. It is expected that the most recent improvements of Pt-based nanoarchitectures will have great ef-fects on the future works for the commercialization of fuel cell catalysts.