Our TEM observation revealed that in a carbon-Pt3Co system, amorphous carbon first crystallized into nanoclusters at step-edges on melting Pt3Co surfaces before merging into graphene layers through a kinetic restructuring via oriented-attachment, leading to the final formation of few-layered graphene nanostructures. The result obtained from density-functional theory calculations further suggested that Co atoms rather than Pt atoms acted as initial nucleation centers.