Abstract: Alkali-excited ground granulated blast furnace slag (GGBFS) can be used in solidification of contaminated soil as an alternative to cement (PC), and has the merits of low energy consumption and low carbon emission. At the same time, the sulfur contained in the GGBFS can reduce hexavalent chromium to trivalent chrome and therefore significantly improve the treat efficiency. Solidification/stabilization (S/S) of a Cr-contaminated soil with the total Cr content of 2000 mg/kg (including 1210 mg/kg Cr(Ⅵ)) is carried out. The treatment by the alkali-excited GGBFS is compared with that by PC. The leaching toxicity, immobilization efficiency and unconfined compressive strength are analyzed to study the treatment effects. The pH, reduction efficiency, chemical morphology, mineral composition and microscopic images are analyzed to investigate the related mechanism. The results show that the leached Cr concentration after treated by the GGBFS is significantly lower than that of the PC. At a GGBFS dosage of 20% and a curing period of 28 d, the leached total Cr and Cr(Ⅵ) decrease to 2.12 and 1.09 mg/L, which meet the regulation limit for landfill disposal. The strength of the GGBFS-treated soil is obviously higher than that of the PC. The valence state analysis shows that S^2- in the GGBFS can effectively reduce Cr(Ⅵ) to Cr(Ⅲ) with a reduction efficiency as high as 96.0%, which avoids the inhibition of Cr(Ⅵ) to the hydration process. The additional reduction agent is not needed when treating such a Cr-contaminated soil with the GGBFS. After the GGBFS treatment, more unstable Cr is transformed to stable forms, and the Cr mobility is significantly reduced. Also, more hydrated gels are generated for cementation of soil particles, resulting in better encapsulation effects and higher strength. This study provides a scientific basis for the S/S of Cr(Ⅵ)-contaminated soil using the GGBFS.