AbstractAcid rain has detrimental effects on the pavement performance of asphalt mixtures. This research investigated the effects of acid-rain immersion on the physical properties and pavement performance of rubber asphalt mixtures containing steel slag; the mechanism behind these effects was also determined. A simulated acid-rain-immersion experiment was designed based on changes in the air voids and Marshall stabilities of the mixtures. Penetration, softening-point, ductility, and viscosity tests evaluated the physical properties of rubber asphalt after acid rain erosion. Rutting, low-temperature bend, and freeze–thaw splitting tests also were conducted. The mechanisms by which acid rain immersion impact the rubber asphalt mixtures containing steel slag were studied via Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. The results revealed that the rubber asphalt becomes brittle and hard after acid rain immersion due to its lightweight components being converted into heavier components due to rubber degradation and asphalt oxidization. Acid rain also reduced the adhesion between the asphalt binder and aggregates by eroding the asphalt film and reacting with components in the steel slag. The results of this research provide reference information for the application of steel slag asphalt mixture in areas affected by acid rain.