Abstract: In order to obtain the influence of corrosion solution on calcium leaching behavior of hardened cement pastes, the deionized water and 6 M NH₄Cl solution were used as corrosion mediums to carry out conventional and accelerated leaching experiments on the cement paste slice specimens with the water-cement ratio of 0.45 at room temperature(25 ℃), respectively.By using the saturation-drying weighing, scanning electron microscopy with energy dispersive spectrometer (SEM/EDS) and X-ray diffraction (XRD), the porosity, microstructure morphology, calcium-silicon mass ratio (Ca/Si)and phase composition of the specimens immersed in two corrosion solutions have been analyzed.Results show that when the room temperature is 25 ℃, compared to the leaching behavior of cement paste slice specimens in deionized water, the leaching rate, characterized by the increasing porosity and the decreasing Ca/Si ratio, of cement paste slice specimens immersed in 6 M NH₄Cl solution has a significant increase.The morphology of the slice specimens after 9-day leaching in 6 M NH₄Cl solution is similar with that of the slice specimen immersed in deionized water for 360 days, while there are basically the same phase compositions of specimens immersed in two corrosion solutions.Thus, 6 M NH₄Cl solution can greatly accelerate the leaching process of hardened cement paste without any alteration to its phase composition and microstructure characteristics during leaching process, and the same leaching characteristics of hardened cement pastes in the deionized water in a relatively short period of time can be obtained.This indicates that NH₄Cl solution can be used as a corrosion medium for accelerating the leaching experiment of cement-based materials.