Abstract: This research investigates one-dimensional unsaturated compression and collapse of intact loess contaminated with different concentrations of sulfuric acid solution. The microstructure and mineral composition were analyzed using SEM and SEM-EDS to reveal the mechanism of acid pollution on the deformation of unsaturated loess. The results showed that the yield stress of 0.05 mol ·L^-1 and 0.5 mol ·L^-1 acid-contaminated loess increased and decreased,respectively,compared to the uncontaminated loess under different suctions. This is because the flocculation of clay in loess plays a dominant role at low-concentration acid pollution,while the dissolution of cementing minerals dominates at high-concentration acid pollution. On the other hand,the permissible void space of the soil structure decreased as the acid concentration increased under a given suction. This is due to the increase in the compression index of the remolded samples and the dissolution of cementing minerals caused by acid pollution. In addition,the measured and calculated collapse potentials were in good agreement for the uncontaminated and 0.05 mol ·L^-1 acid-contaminated samples,while the measured values for the 0.5 mol ·L^-1 acid-contaminated sample deviated from the calculations. This may be because the concentration of pore ionic solution during collapse is significantly lower in the latter case.