A metal-free formylation of imidazopyridines with K2S2O8 via direct decarboxylative cross-coupling of glyoxylic acid is described. This reaction features broad substrate scope, good functional group tolerance, and generate products in good yields. The involvement of radicals in the course of the reaction has been demonstrated by radical trapping experiments with 2,2,6,6-tetramethylpiperidine-1-oxyl and 2,6-di-tert-butyl-4-methylphenol (BHT).