A catalyst- and additive-free sunlight-induced strategy for autoxidation of a wide range of aldehydes to carboxylic acids is described for the first time. In this oxidation system, air serves as the source of oxygen and sunlight as the light source, which include the advantages of green, highly atom-efficient, and low-cost synthesis. This method was easily applied even at gram scale. The reaction proceeds smoothly even at lower temperature and in natural light.