The deterioration of concrete structures due to acid rain is regarded as a long termed phenomenon. Therefore, it is considered that there are many unclear points still on phenomenon and mechanism of it. In this study, it was tried to clarify that the deterioration mechanism on concrete structure due to acid rain. The results are shown as follows; 1) Discoloration of the concrete surface is caused by the formation of ferric sulfate. 2) Elution of alkali metal ions and alkali earth metal ions from the inside of concrete accelerates under the acid rain condition. 3) The neutralization area would extend further depth in concrete due to the diffusion of H₂CO₃, that is formed by the reaction between the acid rain and CaCO₃ existing in the neutralization area in concrete. 4) The corrosion of steel in concrete would be accelerated by not only extension of neutralization area but also the concentration of SO₄^2- and Cl^- from the acid rain at the interface between the neutralization area and the high alkali area of concrete.