Abstract: Melamine-resorcinol-formaldehyde (MR) aerogels were prepared by the sol-gel polymerization of formaldehyde with melamine and resorcinol using NaOH as catalyst, followed by freeze-drying. Co-loaded carbon aerogels were obtained by impregnating the MR aerogels with Co(III) tert-butanol solution, followed by carbonization in N2. The effects of the molar ratios of melamine to resorcinol (M/R), pH, Co content and carbonization temperature on the microstructure of the aerogels were investigated. It was found that the microstructure of the MR aerogels could be adjusted by the M/R ratio and pH. The mesopore size of the MR aerogels decreased with increasing pH and the mesopore size was in the range of 3-4nm when the M/R was 6∶1. There were some graphitic nano-ribbons in Co-loaded carbon aerogels. The metal average particle size in the carbon aerogels increased from 5.2 to 6.2 nm when the carbonization temperature was increased from 700 to 900℃. The electrochemical properties of the Co-loaded carbon aerogels as catalysts in the oxygen reduction reaction were evaluated by a rotating disc electrode technique in an O₂-saturated 0.5 mol/L H₂SO₄ solution, and the catalysts showed a good electrocatalytic activity for the reaction.