Using poly(ethyleneimine) as a source of C and N, FeCl2 as iron and Cl precursor, and SiO2 as template, the first N,Cl-dual-doped mesoporous carbon (denoted as (FeCl2-PEI)(LH)) was prepared. The (FeCl2-PEI)(LH) exhibits a high oxygen reduction electrocatalytic activity and superb durability both in alkaline (0.1 M KOH) and strong acidic (0.5 M H2SO4) solutions, significantly outperforming their counterparts doped with single N due to the synergistic coupling effect arising from the codoping of mesoporous carbon with both N and Cl.