The air oxidations of asphalt at temperatures ranging from 190$circ$C to 270$circ$C were studied for changes in physical properties, proportions and chemical characteristics of asphalt compositions, weak acid and very weak acid contents. The following results were obtained: 1) Oils and resins of asphalt components are oxidized to asphaltenes by blowing(Air oxidation) 2) At 270$circ$C, asphaltenes begin to undergo a change into benzene insoluble after approximately 12 hours of air oxidation. 3) Weak acid increases at the oxidation temperature below 200$circ$C. While very weak acid, presumably phenols, generally increases without regard to the blowing(Air oxidation) temperature.