Visible-light-induced oxidative formylation of N-alkyl-N-(prop-2-yn-1-yl)anilines with molecular oxygen in the absence of an external photosensitizer was developed and afforded the corresponding formamides in good yields under mild conditions. The investigation of the mechanism disclosed that both the starting material and the product act as photosensitizers, and 1O2 and O2˙- are generated through energy transfer and a single electron transfer pathway and play an important role in the reaction.