Infiltration and soak tests were conducted at different pH levels of artificial acid rain to experimentally simulate the erosion process on stabilized soils, which were used for subgrade and base course materials. The authors used three types of lime and cement stabilized soils, and focused on the physico-chemical and engineering behaviors of the eroded soils. Results obtained show that the pH values of the lime and cement stabilized soils generally decreased with continuous infiltration or soak and that these decreases were greater under a higher acid condition. A large reduction of the unconfined compressive strength obtained from the specimens eroded by the higher acid rain was observed in comparison to erosion from the weaker acid rain. In particular, the unconfined compressive strength of the lime stabilized decomposed granite soil (LDGS) eroded by the acid rain with pH 2.0 decreased to 1/6 of its initial value after a small flux of infiltration. The X-ray diffraction patterns show that the straetlingite (2CaO・Al_2O_3・SiO_2・8H_2O) was decomposed, but the gypsum (CaSO_4・2H_2O), calcite (CaCO_3) and unknown chemical crystals were formed in the lime stabilized soils eroded by acid rains with pH 2.0 and 3.0.