5,10,15,20-Tetrakis (4-aminophenyl) Mn-porphyrin and 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde were combined into a new mesoporous organic framework by a Schiff-base-type reaction. Sn(OH)x helped in improving the yield of this Mn-COF. Further, S-containing dimethyl sulfoxide solvent molecules were tripped in the pores of Mn-COFs. Such heteroatoms-enriched Mn-COFs could be used to fabricate Mn-S-N-doped carbons (Mn-S-N-Cs) with abundant mesopores. In particular, Mn-Nx sites could be partly maintained and highly dispersed on the surface of Mn-S-N-Cs; impressively, Mn-N-S-C-800 could be catalyzed for oxygen electroreduction in both alkaline and acidic media. Its half-wave potential reached 0.86 V in 0.1 M KOH, with a very low yield of HO2- (4.02%) and better durability. The thermal conversion of the synthesized mesoporous porphyrinic Mn-COFs provided an efficient strategy for fabricating high-dispersion Mn-Nx sites on mesoporous S and N codoped carbons.