Abstract: The fact that the mechanical properties of clay can be significantly changed by acid and base solutions draws high attention in the study of the mechanical properties of contaminated soils. The change of ionic composition of pore water, soil plasticity, compressibility and strength of the remolded silty clay soaked by sulfuric acid, hydrochloric acid and sodium hydroxide solutions are investigated. The mechanism of the increase of plasticity by sulfuric acid and sodium hydroxide contaminated samples and the decrease of plasticity of hydrochloric acid samples are explained from three aspects: pH value, ion exchange and soil structure. The relationships between mechanical properties and plasticity indexes of the three types of contaminated soils are presented, and they are compared with the empirical formulas for uncontaminated remolded clay. It is found that although the mechanisms are not the same, the three types of contaminated soils show a certain structural effect, which leads to the increase of compressibility. Therefore, the empirical formulas between plasticity and compressibility for uncontaminated remolded clay will underestimate the compressibility of these contaminated samples. However, the structural effect is not sufficient to change the relationship between undrained shear strength c_u and liquidity index I_L, so the strength of contaminated samples can be approximately predicted through the relationship between c_u and I_L of uncontaminated samples.