Multilayer graphenes were synthesized by a mechanochemical treatment of commercial graphite powder and studied as an air electrode for metal-air batteries. The mechanochemical treatment of the commercial graphite powder was performed for 2h using a planetary ball mill apparatus with large stainless steel balls (10 mm diameter) that did not require the aid of solvents. As a result, multilayer graphenes were successfully obtained when the rotational speed of the planetary ball mill was 500 rpm or more. Raman spectroscopy revealed that the resulting multilayer graphenes contains many defects, while electrochemical measurements revealed that this multilayer graphene has high stability against anodic corrosion. Moreover, a higher bifunctional ORR/OER activity was observed for this material than other bifunctional ORR/OER materials, such as LaNiO3 and multilayer graphene synthesized by a modified Hummer’s method. This excellent electrochemical performance implies that the mechanochemically synthesized multilayer graphenes with high stability and high bifunctional ORR/OER activity obtained in this study can be an excellent alternative to carbon black, which is conventionally used for air electrode materials.