Abstract: To evaluate the ameliorative effects of Miscanthus floridulus, a well known heavy metal-tolerant plant species, a bare mine tailing site (control site) and four mine tailing sites (RI, RII, RIII and RIV) inhabited by Miscanthus floridulus on the mine tailing sand were chosen for determining soil microbial biomass, respiration rate and enzyme activities, and the relationships between the microbial parameters. The results showed that except for the pH, soil organic carbon, total nitrogen, total phosphorus, NH4+-N, NO3--N, available phosphorus, aggregate stability and maximum water holding capacity significantly increased (P 0.05) with the inhabitation of M. floridulus, while total or DTPA-extractable heavy metal contents significantly decreased (P 0.05). The inhabitation of M. floridulus signiciantly enhanced soil microbial carbon, nitrogen, phosphorus, basal respiration rate, substrate induced respiration rate and ten enzyme activities, but declinded the phenol oxidase activity and the respiration quotient (P 0.05). The principal components analysis (PCA) showed that soil microbial parameters, physico-chemical and heavy metal properties all significantly discriminated. The canonical correlation analysis (CCA) showed that the net microbial parameters were positively related to the soil physico-chemical properties (except for pH), but negatively related to the heavy metal contents.