Oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalytic activities of p-orbital heteroatom-doped carbon nanomaterials are demonstrated to correlate to the combination of the electron affinity and electronegativity of doping elements, which serves as an activity descriptor for the entire family of p-block element dopants. Such a descriptor has predictive power and enables effective design of new bifunctional catalysts with enhanced ORR/OER activities.