A research program was undertaken to discover the corrosion mechanism of portland cementitious materials to acid rain attack in China. The deterioration process and corrosion products of hardened ordinary portland cement pastes in pH 2 simulated acid rain solution were analyzed by XRD and BSE. The results indicate that the destruction of hardened portland cementitious materials by acid rain attack in China is predominantly due to the coordinated effect of H+ and SO42- of acid rain solution, and gradually occurs from the surface to the interior of materials. The corrosion products are mainly a white mushy mixture consisting of silica gel (SiO2•nH2O), alumina gel (Al2O3•nH2O) and dihydrate gypsum (CaSO4•2H2O) crystal. During the process of acid rain attack, the deteriorated specimen can be divided into corrosion layer, affected layer and unaffected layer.