Isolated single metal atoms have attracted significant attention as catalytic materials with maximum surface areas as well as high activity and selectivity. However, a dense dispersion of single atoms on supported materials has not been achieved. We applied plasma sputtering in N2 atmosphere to disperse single Pt atoms on graphene. Scanning transmission electron microscopy observations confirmed the high-density dispersion of single Pt atoms, without widespread sintering into three-dimensional nanoparticles. X-ray photoelectron spectroscopy measurements revealed that pyridinic nitrogen was selectively doped in graphene during the sputtering. Our novel method provides a simple approach to synthesize high-density single Pt atoms on graphene.