Oxidation of asphalt causes the degradation and failure of asphalt pavement. Due to the molecular complexity and relatively high molecular weight of asphalt, the oxidation mechanism is complicated by the interactions among the molecules of different types. To minimize the interactions, the asphalt sample was chromatographically separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes. These Corbett fractions were then oxidized under ultraviolet irradiation. Fourier-transform infrared spectroscopy was used to analyze the structural changes of the Corbett fractions during photooxidation. All Corbett fractions have shown significant spectral changes in the region of 3500 − 3100 cm−1characterized the stretching vibrations of hydroxyl or nitrogen-hydrogen groups, the peak around 1700 cm−1featured carbonyl groups, and in the region of 1320 − 1000 cm−1characterized the formation of sulfur-containing functional groups. Strong evidence has shown that sulfates are produced in the oxidation of asphalt. The formation of sulfates provides an essential explanation for the deterioration of asphalt pavement.