the present invention relates to a method of preparing a nitrogen - doped graphene comprising preparing a edge - functionalized graphene by binding a graphite with a organic material having amino groups and functional groups such as carboxy acid group through an electrophilic substitution reaction , and heat treating the resultant edge - functionalized graphene , and a nitrogen - doped graphene prepared thereby . according to the present invention , by a more inexpensive and simpler method , a nitrogen - doped graphene can be prepared at higher purity and higher yield . the nitrogen - doped graphene obtained by the present invention has very excellent physical and electric properties , and particularly has a superior oxygen reduction capability , compared with the platinum catalyst used at cathode of a h 2 / o 2 fuel cell so that it will replace the platinum to lower more the cost of a h 2 / o 2 fuel cell or to increase its life and further to provide a new turning point for the commercialization of a h 2 / o 2 fuel cell .