Uniaxial compression test and mercury injection test are conducted on argillaceous cemented sandstone corroded in solutions with different pH values by using MTS816 servo system and mercury intrusion porosimeter. The influences of pH value on strength degradation and microstructure of rock are examined. The results are concluded as follows: (1) acid or alkaline solution both weakens the mechanical strength of rock, and especially when pH value equals 6 and 9, the strength degradation rate reaches the maximum. (2) When pH value reaches 9 and continues to grow, or reduces to 6 and continues to drop, the strength degradation rate is rarely affected. (3) When pH value decreases from 6 to 2, the peak strength of rock declines from 76.94 MPa to 70.91 MPa, with the degradation rate amounting to 7.83%; when pH value increases from 7 to 10, the peak strength reduces from 79.89 MPa to 64.41 MPa, and the degradation rate is 18.12%; when pH value further increases from 10 to 12, the peak strength drops from 64.41 MPa to 63.00 MPa, with a degradation rate only 2.19%. (4) Despite the increase or decrease of pH value, the porosity and skewness of argillaceous fine sandstone tend to rise. The proportion of small opening with diameter less than 0.1 μm experiences the greatest change, and is, meanwhile, the major microcosmic factor that decides the degradation of mechanical strength of the corroded rock. The quantified influence of pH value on the mechanical properties and microstructure of rock would offer new idea and approach for researches on the safety and stability of water-involved rock engineering field.