Provided are a method of preparing a graphene quantum dot, a graphene quantum dot prepared using the method, a hardmask composition including the graphene quantum dot, a method of forming a pattern using the hardmask composition, and a hardmask obtained from the hardmask composition. The method of preparing a graphene quantum dot includes reacting a graphene quantum dot composition and an including a polyaromatic hydrocarbon compound and an organic solvent at an atmospheric pressure and a temperature of about 250° C. The polyaromatic hydrocarbon compound may include at least four aromatic rings.