Iron−nitrogen−carbon (Fe−N−C) materials emerged as one of the best non-platinum group material (non-PGM) alternatives to Pt/C catalysts for the electrochemical reduction of O 2 in fuel cells. Co-doping with a secondary metal center is a possible choice to further enhance the activity toward oxygen reduction reaction (ORR). Here, classical Fe−N−C materials were co-doped with Sn as a secondary metal center. Sn−N−C according to the literature shows excellent activity, in particular in the fuel cell setup; here, the same catalyst shows a nonnegligible activity in 0.5 M H 2 SO 4 electrolyte but not as high as expected, meaning the different and uncertain nature of active sites. On the other hand, in mixed Fe, Sn−N−C catalysts, the presence of Sn improves the catalytic activity that is linked to a higher Fe− N 4 site density, whereas the possible synergistic interaction of Fe−N 4 and Sn−N x found no confirmation. The presence of Fe−N 4 and Sn−N x was thoroughly determined by extended X-ray absorption fine structure and NO stripping technique; furthermore, besides the typical voltammetric technique, the catalytic activity of Fe−N−C catalyst was determined and also compared with that of the gas diffusion electrode (GDE), which allows a fast and reliable screening for possible implementation in a full cell. This paper therefore explores the effect of Sn on the formation, activity, and selectivity of Fe−N−C catalysts in both acid and alkaline media by tuning the Sn/Fe ratio in the synthetic procedure, with the ratio 1/2 showing the best activity, even higher than that of the iron-only containing sample (j k = 2.11 vs 1.83 A g −1 ). Pt-free materials are also tested for ORR in GDE setup in both performance and durability tests.